The IRS has very specific annual tax filing requirements for nonprofit organizations.
501c3 public charities must complete the form 990, 501c3 private foundations must complete the form 990 pf, and nonprofits that make $25,000 or less per year must complete a form 990-N.
According to the IRS if small organizations failed to file a form 990-N for the past three years, on May 15th their tax exempt status will be REVOKED. Guidestar estimates that between 350-400k nonprofits will loose their tax exempt status!! Yikes.
Here are some tips and resources on quarterly and annual filing requirements for nonprofits.
1. Don't overlook letters from the IRS (seriously)
2. File annual 990's
3. File annual paperwork with the state attorney general's office
4. File quarterly wage and tax statements (check with your state)
FREE Handbook from Southern California Edison: Legal Issues for Small Businesses and Nonprofit Agencies
Form 990 Resources and Tools
Nonprofit Law Blog
Not for Profit Accounting Blog
Exempt Employer's Toolkit