How nexus works: economic vs. physical triggers
Nexus is the legal connection that gives a state the authority to require you to collect and remit sales tax. Since the Supreme Court's 2018 ruling in South Dakota v. Wayfair, [3] states have been free to enforce nexus on two independent bases: physical presence (the older standard) and economic activity (the newer one). Most mid-market ecommerce brands carry both, often in the same states, and the two trigger by different mechanics on different timelines.
We've noticed a pattern with brands coming to us in the $20-80M range. They understand they have economic nexus, but they haven't mapped their physical nexus. A 3PL relationship in Pennsylvania, FBA inventory in California, a remote hire in Colorado, all created obligations that started the day the activity began, not the day the brand realized it. Economic thresholds at least announce themselves through volume. Physical triggers do not.
Start with the foundational distinction, then layer the threshold mechanics on top:
The second question, what counts toward the threshold, is where most brands get the calculation wrong. Marketplace sales, exempt sales, and shipping charges are treated differently in different states. A brand that includes marketplace sales in its threshold check can over-register, while one that excludes them in a state that includes them can under-register.
State threshold mechanics
The 50-state threshold matrix is the operational reference for any brand mapping its current and projected footprint. Most states settled near the original Wayfair standard ($100,000 or 200 transactions), but the variance matters.
California, Texas, and New York set theirs at $500,000, which means a $400k seller into California has no economic nexus there but does have it in any standard-threshold state. New York uses an AND test (both $500,000 and more than 100 transactions) rather than the OR test most states use. Several states have repealed the 200-transaction prong entirely, including California, South Dakota, and Wisconsin.
Marketplace facilitator laws sit alongside the threshold matrix and determine who collects the tax when a sale runs through Amazon, Walmart, eBay, or another marketplace. In every state with a facilitator law, the marketplace collects on the seller's behalf for marketplace sales. Whether those sales still count toward the seller's threshold for direct-sales registration varies state by state.
Businesses often rely on providers such as TaxCloud to monitor changes in nexus thresholds and marketplace facilitator rules as states update their requirements.
Inventory and physical-presence triggers
Physical nexus is where the surprises live.
Three triggers come up repeatedly in operator conversations: FBA inventory, 3PL inventory, and remote employees. Each creates nexus the day the activity begins, not the day the brand finds out about it, which means lookback exposure starts ticking immediately. [5]
FBA inventory creates physical nexus in the states where Amazon stores your goods, which is determined by Amazon's fulfillment network, not by any decision you made. A brand listing through FBA can have inventory in 15+ states without ever choosing those states. Some states have softened FBA-driven nexus enforcement in recent years (Pennsylvania most notably), and others have not.
3PL warehouses follow the same logic. If your 3PL operates a fulfillment center in Pennsylvania, your inventory in that warehouse is physical presence in Pennsylvania, regardless of where your office or your sales channels sit. Brands that migrate from a single-warehouse setup to a multi-node fulfillment network often pick up 3 to 6 new physical-nexus states in a single quarter.
Remote employees are the third common trigger. Hiring a customer service rep, a developer, or any W-2 employee in a new state generally creates physical nexus there, regardless of role. The pandemic-era expansion of remote hiring quietly created physical-nexus footprints for thousands of brands that had no idea.
Monitoring nexus exposure at scale
For a brand with 25 to 40 active states, monitoring is the work, not the registration. Thresholds change. New states pass new rules. A new 3PL location, a new remote hire, or a new wholesale channel can move the footprint without anyone in finance hearing about it. The brand that monitors quarterly finds problems while they are still cheap. The brand that monitors annually finds them after they have compounded.
The single most common monitoring failure we see: a brand treats Shopify Tax's threshold view as its full nexus footprint. Shopify Tax tracks Shopify orders. A brand running Shopify plus Amazon plus wholesale through Faire is seeing roughly half its volume in the threshold view, and the other half is invisible to it. The view is a useful starting point. It is not the answer.
Threshold monitoring is only as accurate as the data it can see. Businesses selling across multiple channels need a consolidated view of sales activity to identify where nexus thresholds are approaching, have been crossed, or no longer apply.
Remediation: when you discover exposure you didn't track
When a brand discovers it crossed nexus thresholds in states where it never registered, the question is not whether to act. It is which path. Two operational questions structure the remediation:
- How much exposure exists, state by state?
- Is the right path a voluntary disclosure agreement (VDA) or a standard registration with a current-date effective date?
The exposure quantification has to come first because the path decision depends on it. A state with $4,000 of estimated back-tax usually isn't worth the VDA process. A state with $80,000 of back-tax almost always is, because the VDA caps lookback (typically at 3 to 4 years) and waives penalties in exchange for the voluntary disclosure.
If the brand receives a nexus inquiry letter from a state before it has acted on remediation, the timeline changes. See responding to a state nexus inquiry letter in the audit category, where letter response sits operationally.
Where nexus fits the operating model
Nexus mapping is the foundation that the rest of compliance sits on. Registration cadence, filing volume, exemption-certificate workflow, and audit defense all start from an accurate nexus footprint, and a wrong footprint propagates downstream. A brand that under-registers will under-file and face lookback enforcement later. A brand that over-registers will pay filing fees on states it never owed.
Native Shopify and Shopify Plus integration handles the calculation and order-data layer. Registration and filing operations sit on top of it. The architecture point is that nexus monitoring, registration, calculation, and filing live in one connected layer instead of four disconnected tools.