In a revised guide for taxpayers, the Internal Revenue Service explains the rules that tax-exempt organizations must follow when they raise money through business activities.

Charities and other nonprofit groups must pay unrelated-business income tax, known as UBIT, on retail sales, magazine publishing, and other commercial operations that are not directly related to their missions.

The tax agency’s updated Publication 598 explains which organizations are subject to the tax; what an unrelated trade or business is; and how groups should calculate their unrelated-business taxable income.