Tax-exempt organizations using the calendar year as their fiscal year must file 2013 990-series information returns and notices by Thursday, May 15, and should be careful about the information they include, the IRS warned.

Small tax-exempt organizations with average annual receipts of $50,000 or less may file the e-notice 990-N (e-Postcard), which asks for a few basic pieces of information. Tax-exempt organizations with average annual receipts exceeding $50,000 must file a 990 or 990-EZ depending on their receipts and assets. Private foundations file a 990-PF.

The Pension Protection Act of 2006 mandates that most tax-exempt organizations file annual 990-series informational returns or notices. Organizations that fail to file annual reports for three consecutive years have their federal tax exemptions automatically revoked.

The IRS also warned groups filing in May not to include Social Security numbers or other unneeded personal information on their 990 and to consider e-filing. By law, both the IRS and most tax-exempt organizations are required to publicly disclose most parts of form filings, including schedules and attachments; tax-exempt forms that must be made public include the 990, 99-EZ and 990-PF, among others. Public release of SSNs and other personal information about donors, clients or benefactors could open the door to ID theft, the service warned.

Organizations that need additional time to file a 990, 990-EZ or 990-PF may obtain an extension. No extension is available for filing the 990-N.