Even though an organization is recognized as tax exempt, it still may be liable for tax on its unrelated business income. For most organizations, unrelated business income is income from a trade or business, regularly carried on, that is not substantially related to the charitable, educational, or other purpose that is the basis of the organization’s exemption. An exempt organization that has $1,000 or more of gross income from an unrelated business must file Form 990-T. An organization must pay estimated tax if it expects its tax for the year to be $500 or more.
The obligation to file Form 990-T is in addition to the obligation to file the annual information return, Form 990, 990-EZ or 990-PF. Each organization must file a separate Form 990-T, except title holding corporations and organizations receiving their earnings that file a consolidated return under Internal Revenue Code section 150. Source: Unrelated Business Income.
However, there are some exceptions. For additional Information on these exceptions go to: Unrelated Business Income Tax Exceptions and Exclusions