This is viewed as circumventing U.S. payroll tax rules. An employee who exceeds the commercial traveler limits, and who is not from a treaty country, is subject to U.S. income taxes on his compensation for U.S. services. No doubt hundreds of thousands of B-1 visitors to the United States each year exceed these rules and are subject to U.S. income taxes without becoming aware of the obligation. Tax Residency Rule A B-1 visitor's U.S. presence can have much more dire tax consequences. Under the U.S. tax rules, a visitor who spends 183 days or more in the United States in the calendar year or 183 days based on a formula is a resident for U.S. tax purposes.
Vacation days count as well as business days.
Partial days, such as the arrival day and departure day, count as a full day in the formula. If the visitor's U.S. days exceed 30 days in the current year, and the result of the formula is 183 days or more, the visitor is a resident for U.S. tax purposes. A resident is subject to U.S. income taxes on worldwide income. In order to avoid this result, a business visitor must average less than 122 U.S. days per calendar year unless an exception applies. One exception allows a visitor who is present less than 183 days in the calendar year but whose presence over the current year and two prior years equals or exceeds 183 days to avoid U.S. tax resident status if the visitor has a tax home in a foreign country for the full calendar year, and the visitor can prove a closer connection to a foreign country for the calendar year.