Ecommerce sales tax compliance rules vary by business structure, sales channel, and state. The guidance here is general. For obligations specific to your business, speak with a qualified sales tax specialist.
A seven-figure seller we know got a letter from Illinois asking for three years of sales data. She hadn’t set out to ignore her taxes. She crossed an economic nexus threshold in year two and never registered. By the time the letter arrived, past due sales tax penalties, compounding interest, and back taxes had turned her original obligation into a number much larger than she expected.
She told us: “I always figured I’d deal with sales tax later.”
Later had already happened.
If you’re running a seven or eight-figure ecommerce brand on Shopify or Amazon, this guide walks you through what actually happens when sales tax goes unpaid, how states find non-compliant sellers, and the legal tools available to fix it before things escalate.
- What Is Sales Tax Nexus?
- Why Ecommerce Sellers Fall Behind
- How States Find Non-Compliant Sellers
- How Past Due Sales Tax Penalties Stack Up
- Two Real Exposure Scenarios
- How to Fix Past Due Sales Tax Obligations
- Frequently Asked Questions
Key Takeaways:
- Sales tax obligations begin the day you cross a nexus threshold, not the day you discover you crossed it
- There are two types of nexus: physical nexus (warehouse, office, FBA inventory) and economic nexus (usually $100K+ in annual sales into a state).
- Amazon FBA sellers have physical nexus in every state holding their inventory, even states they have never visited.
- Amazon’s marketplace facilitator collection only covers Amazon transactions. Shopify stores, wholesale channels, and other platforms are the seller’s responsibility.
- Multi-channel sellers must count all sales channels together when calculating economic nexus thresholds.
- A $20,000 back tax balance in one state can grow to $28,000 to $32,000 after late filing penalties, late payment penalties, and compounding interest.
- States actively find non-compliant sellers through pre-audit surveys, Amazon data requests, cross-state data sharing, and third-party seller lists.
- Ignoring a pre-audit survey almost always triggers a full audit.
- Filing a return, even without full payment, stops one penalty clock immediately.
- A Voluntary Disclosure Agreement (VDA) is the most effective resolution tool. It caps the lookback period and can eliminate penalties, but only if initiated before the state contacts you first.
- Business owners can be held personally liable for unpaid sales tax, since it is classified as a trust fund tax.
- A nexus analysis across all states, channels, and inventory locations is the critical first step before taking any corrective action.
What Is Sales Tax Nexus?
Nexus is the legal term for a connection to a state that requires you to collect and remit sales tax there. Once you have it, you have an obligation. Miss it, and the clock on past due sales tax penalties starts the day you crossed the threshold, not the day you find out about it.
There are two types every ecommerce seller needs to understand.
Physical Nexus means a real presence in a state:
- An office, employees, or a warehouse
- Inventory stored in that state
- For Amazon FBA sellers: any fulfillment center holding your products counts, even in states you’ve never visited
Economic Nexus came out of the 2018 Supreme Court ruling in South Dakota v. Wayfair:
- If your total sales into a state cross a certain threshold, you owe sales tax there regardless of physical presence.
- Most states set that threshold at $100,000 in annual sales.
- For multi-channel sellers, your Amazon sales, Shopify sales, and every other channel count toward that number together.
| Nexus Type | What Triggers It | Common Ecommerce Example |
| Physical Nexus | Office, warehouse, inventory, or employees in a state | FBA inventory stored in a fulfillment center |
| Economic Nexus | Exceeding a state’s annual sales threshold | $100K+ in total sales into that state |
Why Ecommerce Sellers Fall Behind on Sales Tax Compliance
Most sellers don’t fall behind on ecommerce sales tax compliance because they’re ignoring it. They fall behind because they grew faster than their compliance did.
It usually goes like this:
- You start selling in one state and you’re fine.
- Revenue crosses $100,000 in a second state and you’re not watching for it.
- You scale your FBA operation and inventory spreads across eight fulfillment center states.
- You add a Shopify store on top of Amazon.
Now you have nexus in twelve states. You’re registered in two.
That gap between where you’re registered and where you should be registered is your exposure. And the clock on that gap started the day you crossed each threshold, not the day you discovered the problem.
There’s also a persistent misconception worth naming directly: many Amazon sellers believe that because Amazon collects and remits sales tax through marketplace facilitator laws, they’re fully covered. They’re not, and the reason matters. More on this in the scenarios section below.
How States Find Non-Compliant Sellers
States are not waiting for sellers to come forward. They’ve built systems specifically to find who should be filing but isn’t.
- Pre-audit surveys. Washington, Illinois, Massachusetts, New York, Maine, Arizona, Michigan, and Wisconsin have been active in sending letters requesting up to three years of sales data, even to sellers who aren’t registered in that state. Ignoring these letters almost always triggers a full audit. Non-response is treated as a red flag.
- Amazon data requests. States can legally request seller data directly from Amazon, including your sales volume, seller ID, and which fulfillment centers held your inventory. That data gets cross-referenced against state registration records.
- Cross-state data sharing. If one state opens a case on you, they can share your data with neighboring states. Illinois actively requests sales data from neighboring states during their own audit process. One compliance gap can quickly become four separate problems.
- Third-party seller lists. States including Utah and Connecticut purchase lists of online sellers from third-party data providers and run those against their own registration records to identify who should be filing but isn’t.
How Past Due Sales Tax Penalties Stack Up
Three separate charges layer on top of each other, and they compound over time.
| Penalty Type | Typical Rate | Applied to $20,000 Owed |
| Late Filing Penalty | 5 to 25% of tax owed | Up to $5,000 |
| Late Payment Penalty | 5 to 10% of tax owed | Up to $2,000 |
| Annual Interest | 5 to 12%, compounding | $3,000 to $5,000 over 2 to 3 years |
| Total Possible Liability | $28,000 to $32,000 |
A $20,000 back tax obligation in a single state can reach $28,000 to $32,000 once penalties and two to three years of compounding interest are added. Multiply that across four states and the math changes fast.
One thing worth knowing:
- File even if you can’t pay the full balance. A filed return with no payment is significantly better than no return at all
- Late filing penalties and late payment penalties are charged separately
- Filing stops one of those clocks immediately
- States typically escalate faster on unfiled returns than on unpaid balances
Two Real Exposure Scenarios
The FBA Seller Who Thought Amazon Had It Covered
Amazon does collect and remit sales tax on transactions made through their platform. That’s true and it matters. But it doesn’t cover everything.
Here’s what sellers miss:
- Physical nexus still applies. FBA inventory creates physical nexus in every fulfillment center state. States like Washington and Pennsylvania require registration and filing even when the return is for zero dollars.
- Amazon’s coverage stops at Amazon. Your Shopify store, your wholesale channel, any other platform are your responsibility entirely.
- Amazon’s data helps states find you. Amazon’s marketplace facilitator filing gives states a list of every seller using FBA and which states their inventory is in. While Amazon handles collection, it also makes it easier for states to identify unregistered sellers.
An FBA seller doing $3 million a year across Amazon and Shopify, with inventory in eight fulfillment center states, has real exposure if registrations aren’t in place and Shopify sales aren’t being managed.
The Shopify Seller and the Texas Problem
A Shopify seller crosses $500,000 in Texas sales in year three and never registers. Here’s how the math works out:
- Texas has a 20% late filing penalty.
- A separate late payment penalty applies on top of that.
- Texas compounds interest monthly.
A $25,000 back tax obligation can reach $38,000 to $45,000 by year six. And if Texas finds that seller because Illinois shared data during a separate audit, they’re not starting with a gentle letter.
Neither of these sellers did anything malicious. They grew fast and compliance didn’t keep up. That’s the most common version of this story.
How to Fix Past Due Sales Tax Obligations
The earlier you act, the better the outcome. That is consistently true. Here are the tools available.
Voluntary Disclosure Agreement (VDA)
A VDA is the most powerful option for sellers who haven’t been found yet. Here’s how it works:
- You approach the state before they find you and voluntarily disclose your back tax obligations.
- Most states limit how far back they look, typically three to four years instead of your full exposure window.
- States often reduce or eliminate penalties entirely in exchange for voluntary disclosure.
- A $50,000 problem can become a $20,000 problem through a well-executed VDA.
The word “before” is doing a lot of work here. If the state finds you first, the VDA option closes permanently.
Payment Plans
If you can’t pay the full balance upfront:
- Most states will negotiate a payment plan.
- Interest continues during the plan, but it keeps your business in good standing.
- Payment plans prevent bank levies and keep your business operating.
- States typically want all outstanding returns filed before agreeing to a plan. Get clean on filings first, then negotiate the payment.
Penalty Abatement
In some cases, you can formally request penalty removal:
- Works best with a solid prior compliance history.
- Also considered when there’s a documented reason for the gap, such as a software failure or significant business disruption.
- Interest is harder to remove, but penalties are worth requesting when the underlying tax amount is significant.
Start With a Nexus Analysis
Before any of this, you need a clear picture of where you actually have nexus. A proper nexus analysis:
- Looks at every state, every sales channel, and every inventory location.
- Gives you real obligations, not rough guesses.
- Lets you prioritize highest-exposure states first.
- Makes everything else on this list more manageable.
Frequently Asked Questions
What happens if I ignore a pre-audit survey from a state? Ignoring a pre-audit survey almost always triggers a full audit. States treat non-response as a red flag. If you haven’t actually crossed that state’s nexus threshold, a clean documented response can end the process before it starts. If you have crossed it, ignoring the letter makes the outcome significantly worse.
Does Amazon handle all my sales tax obligations? No. Amazon collects and remits sales tax on transactions made through their platform under marketplace facilitator laws. It does not cover sales through your Shopify store, wholesale channels, or other platforms. FBA inventory also creates physical nexus obligations in fulfillment center states that exist independently of Amazon’s collection.
What is a voluntary disclosure agreement for sales tax? A VDA is a legal agreement where you proactively disclose unpaid sales tax to a state before they find you. In exchange, most states limit the lookback period and reduce or waive penalties. It’s the most effective way to reduce total liability and must be initiated before the state contacts you first.
Can states audit further back than three years? Most states have a three-to-four-year statute of limitations for sales tax audits. However, if you were never registered, some states can look back further. A VDA typically caps the lookback at three to four years regardless of how long the obligation has existed.
Can I be personally liable for my business’s unpaid sales tax? Yes. Sales tax is a trust fund tax. The legal theory is that you collected it from customers on behalf of the state. In many states, if your business cannot pay what it owes, the state can pursue business owners personally. At the seven and eight-figure level, this is one of the highest-stakes aspects of non-compliance.
Know Where You Actually Stand
If this raised questions about your business, the first step is getting a real picture of your nexus footprint, not a rough guess.
LedgerGurus built a free Sales Tax Risk Assessment for exactly this:
- 18 questions, takes about five minutes
- Get your current risk level
- See a breakdown of what needs attention across your nexus footprint
- Walk away with a prioritized action plan
It’s built for sellers doing $1M to $50M who aren’t fully certain they’re registered everywhere they should be.
Take the Free Sales Tax Risk Assessment →
Want to talk through your situation directly? LedgerGurus specializes in ecommerce sales tax for seven and eight-figure brands, including nexus analysis, VDA negotiations, back filings, audit support, and ongoing compliance. Reach out here.
