A contractor based in one state takes three jobs across a border over a summer. Two years later an envelope arrives from that state's revenue department asking about unregistered activity, unfiled returns, and tax that should have been collected on materials. The work was legitimate, the income was reported federally, and none of that is what the letter is about.
State and local obligations are where small operations get caught, and it is not because owners are careless. It is because there is no single rulebook, no single agency, and nothing that tells you a duty has started.
Why there is no single answer
The federal government levies income tax and the payroll taxes attached to it. Everything else is decided separately by fifty states and, beneath them, by counties, cities, and in some places special districts that exist for a single purpose such as transit or a stadium.
Each of those layers can impose its own tax, its own registration, and its own filing calendar. A single address can sit inside four overlapping jurisdictions with four different rates and four different due dates. That is not a flaw somebody forgot to fix. It is the design, and it is why a national answer to a state question does not exist.
The practical consequence is that advice from a friend in another state is worthless, and confidently wrong advice is common precisely because everyone's experience is local.
What creates an obligation in a state
The general concept is a connection substantial enough that a state can require you to register and collect. Physical presence is the clearest version: an office, a warehouse, inventory stored there, an employee working there, or in many states performing services within the state at all.
Deliveries in your own vehicle count in a way that shipping by common carrier often does not. Storing tools or materials in a rented space counts. Sending a crew for two weeks counts in many places. And for sellers with no physical presence, most states now set thresholds based on sales volume or number of transactions into the state, which is how online sellers acquire obligations in states they have never visited.
The safest habit is to ask the question before the first job in a new state rather than after, because registering in advance is a form and registering late is a negotiation.
The three that catch small operations
Whether services are taxable is the first. Many people assume sales tax applies to goods only. Some states tax a long list of services, some tax a short one, and some tax repair and installation labor while exempting new construction. Getting this wrong means you never charged the customer, and the state will still want the money.
Use tax is the second and it is the least known of all. When you buy something without paying sales tax, typically from an out of state supplier, and then use it in your own state, you generally owe the equivalent tax directly. Small operations buying tools and materials online accumulate this without ever knowing the category exists.
Local licensing is the third. Plenty of cities and counties require a business license, and some require one from every city you work in rather than the one you are based in. The fees are usually small. The penalties for years of not having one are not always small, and an unlicensed business can find a contract unenforceable in some places.
What the letter usually says
Typically that the state believes you had activity there, that no returns are on file, and that you should respond by a date. Often it is triggered by something ordinary: a customer claimed an exemption and named you, a competitor complained, or a permit was pulled in your name.
Answer it. These letters escalate on a schedule and they do not go away. The first response is normally straightforward, establishing what you actually did, in which years, and for what amounts. The federal government's public directory of state and local agencies is the fastest way to find the right office and confirm you are dealing with the real one, which matters because tax notices are also a favorite template for scams.
Getting current without making it worse
Most states run a voluntary disclosure process. A business that comes forward before being contacted typically gets a limited look back period and reduced or waived penalties, in exchange for registering and paying what is owed for that window. It is a well worn path and states use it because they would rather have a registered taxpayer than an argument.
The order that works is: find out what you owe before you announce yourself, usually with an accountant who handles multistate work, then approach through the disclosure program rather than by filing a stack of late returns and waiting. Once a state has contacted you, that door generally closes, which is why the letter arriving is the expensive version.
The habit that prevents all of this is unglamorous. Before the first job in any new city or state, spend twenty minutes on that jurisdiction's revenue and licensing pages. It is the cheapest twenty minutes in the business and it turns a two year problem into a form.