Multi-State Sales Tax Nexus: What Actually Triggers a Filing Obligation

Sales tax nexus used to be a simple question tied to physical presence: if you had a store, an office, or an employee in a state, you collected and remitted sales tax there, and otherwise you generally did not have to think about it. That framework changed permanently with the Supreme Court's 2018 Wayfair decision, which allowed states to impose sales tax collection obligations based on economic activity alone, no physical presence required, and most states moved quickly to adopt economic nexus thresholds of their own. A business can now owe sales tax registration and collection obligations in a state it has never set foot in, purely because of how much revenue or how many transactions it generated there.

Economic nexus thresholds vary by state but commonly follow a pattern: a dollar amount of sales into the state, a number of separate transactions, or either one triggering the obligation. Historically many states used a combined test, for example, a revenue threshold or a transaction-count threshold, whichever came first, though a number of states have since simplified or raised these thresholds. The specific numbers, and whether a state uses a revenue test, a transaction test, or both, differ enough from state to state that a business selling into multiple states cannot assume the same threshold applies everywhere.

The trigger is often revenue you were not tracking for this specific purpose. A business that ships product nationally, sells through its own e-commerce site, or serves clients remotely across state lines can accumulate meaningful sales into a state without anyone at the company realizing a threshold was crossed, because the internal reporting was organized around total revenue or by customer, not by state-level breakdown. The first sign of a problem is often a notice from a state department of revenue, well after the exposure has been accumulating.

Marketplace facilitator rules complicate the picture further for businesses that sell through platforms like Amazon, Etsy, or similar marketplaces. In most states, the marketplace itself is now responsible for collecting and remitting sales tax on transactions it facilitates, which can reduce a seller's direct registration burden for marketplace sales specifically. But sellers who sell both through a marketplace and through their own direct channels need to track these separately, because marketplace-facilitated sales and direct sales are not always treated identically for nexus threshold calculations, and assuming the marketplace "handles everything" can leave a real gap on the direct-sales side.

What counts as a taxable sale is its own layer of complexity once nexus is established. Physical goods are broadly taxable in most states, but services, digital products, and software-as-a-service are taxed inconsistently, taxable in some states, exempt in others, and subject to different rules depending on how the product is delivered or used. A SaaS company can have registration obligations in a dozen states and taxable status in only some of them, which means nexus determination and taxability determination are two separate analyses that both need to happen correctly.

Registration itself is not something to delay once an obligation is identified, and the sequencing matters. Registering for sales tax in a state generally requires setting up withholding accounts, filing frequency elections, and in some cases retroactive filings for periods where the obligation existed before registration was completed. States vary in how aggressively they pursue retroactive liability, but voluntary disclosure programs exist in most states specifically for businesses that come forward proactively before an audit finds them, typically offering a shorter lookback period and reduced penalty exposure compared to discovery through enforcement.

Income tax nexus is a related but separate question that often gets confused with sales tax nexus, and the two do not always move together. A business can have sales tax collection obligations in a state without necessarily having income tax nexus there, and vice versa, depending on the state's specific rules for each tax type and any applicable protections like Public Law 86-272 for certain income tax situations. Treating "nexus" as one unified concept across tax types is a common and costly oversimplification.

Remote employees have become one of the more common and least understood nexus triggers in the post-2020 environment. A single remote employee working from a state where the business has no other presence can create nexus for income tax, sales tax, and payroll tax purposes simultaneously, depending on the state and the employee's role. Businesses that expanded their remote workforce without revisiting their multi-state tax footprint often discover this exposure well after the hiring decision, when a routine review or a state inquiry surfaces it.

Software exists to automate sales tax calculation, filing, and remittance across jurisdictions, and for businesses with meaningful multi-state exposure, it is generally worth the cost relative to manual tracking. But software solves the mechanical filing problem. It does not solve the upstream question of where you actually have an obligation in the first place, which still requires a periodic review of revenue by state against each state's current thresholds and rules.

The practical starting point for any business unsure of its exposure is a nexus study: a structured review of revenue by state, transaction counts, remote employee locations, and marketplace activity, compared against current thresholds in every state where activity exists. This is not a one-time exercise, thresholds change, your revenue mix changes, and a state where you were comfortably under the threshold two years ago may not be today.

OICPA runs nexus studies for growing businesses, prioritizes the states with the highest exposure first, and coordinates registration sequencing, including voluntary disclosure where it is the better path. So multi-state growth does not turn into a compliance backlog discovered by a state notice instead of by your own review.