Operating across state lines creates registration and tax obligations that are easy to trigger and easy to miss.

Qualification to do business. Required where the entity transacts business in the state, a term defined by exclusion in most statutes — maintaining bank accounts, holding meetings, and isolated transactions do not count; employees, offices, property and a regular course of business do.

Consequences of failure. Inability to bring suit in the state’s courts until qualified, back fees and penalties, and in a few states contract unenforceability. Defendants raise it as a threshold defense.

Income tax nexus. Physical presence, and increasingly economic nexus based on receipts thresholds. Federal law protects solicitation of orders for tangible goods where the orders are approved and filled outside the state — a narrow protection that does not cover services, licensing or most modern business models.

Sales tax nexus on economic thresholds following the abandonment of the physical presence requirement, with registration, collection and filing obligations in every state where the threshold is met.

Employment. A single employee generally creates withholding, unemployment insurance and workers compensation obligations.

Practical approach. A periodic nexus review as the business grows, because the obligations accrue whether or not anyone noticed.