Before 2018, you only had to collect sales tax in states where your business had a physical presence. A warehouse, office, employee, or even inventory stored in a fulfillment center could create that obligation. But selling to customers across state lines from your home office or through a website? No requirement to collect their state’s sales tax.

The Supreme Court’s ruling in South Dakota v. Wayfair changed everything. The court decided that economic activity alone could create a sales tax collection obligation, even without any physical connection to a state. This concept is called economic nexus.

Now most states require you to collect and remit sales tax once you exceed certain thresholds within their borders. The common threshold is $100,000 in sales or 200 transactions within a calendar year, though some states have dropped the transaction count and only use the sales amount. Each state sets its own rules and can change them at any time.

For online sellers, this created a significant compliance burden. A business selling nationwide might trigger nexus in dozens of states. Each state has different tax rates, different rules about which products are taxable, different filing frequencies, and different registration requirements. You can’t just collect one rate and send it somewhere.

The practical impact depends on your business model. If you only sell locally within Massachusetts and the Merrimack Valley, the Wayfair decision might not affect you directly. If you sell through Shopify, Amazon, or your own website to customers across multiple states, you’re likely dealing with economic nexus in several jurisdictions right now.

Tracking where you’ve crossed thresholds requires ongoing monitoring. You need to know your sales by state, register with tax authorities when you hit thresholds, configure correct rates in your sales platform, file returns on each state’s schedule, and keep up with rule changes. A small business bookkeeping service can help track your state-by-state sales and flag when you’re approaching nexus triggers.

Software like TaxJar or Avalara can automate calculations and filing, but only if someone configures it correctly and monitors threshold crossings. The software doesn’t handle registration or catch errors without proper oversight.

If you’re already selling in multiple states and haven’t addressed sales tax compliance, you may have back-tax exposure. States are increasingly aggressive about finding out-of-state sellers who should be collecting. Getting compliant now is better than receiving a notice and owing years of uncollected tax plus penalties.