May 17, 2010, is the deadline for nonprofit corporations that are tax exempt organizations (other than churches) with less than $25,000 in income to file IRS form 990-N.  A change in the law three years ago become effective on May 17th.  See “Thousands of nonprofits may lose tax-exempt status” and “Thousands of non-profits could unwittingly lose tax status.”

See the article in the Nonprofit Law Blog called “The End of Small Nonprofits That Have Not Filed Form 990.”