Just because you are a not-for-profit doesn’t mean you don’t have to file a tax return. Once your receipts (all the money you take in from any source) exceed $25,000, you need to file a return. You may also owe tax on any unrelated business income.
Word of warning - do not fool around with IRS requirements. Be diligent about filing the required paperwork and paying appropriate taxes. Many an organization has gotten itself in considerable hot water by not adhering to stated requirements and had its nonprofit status threatened.
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