For tax years ending on or after December 31, 2007, certain corporations (entities) with reasonable cause for not timely filing Form 2553 can request to have the form treated as timely filed by filing Form 2553 as an attachment to Form 1120S, U.S. Income Tax Return for an S Corporation. An entry space for an explanation of reasonable cause was added to page 1 of the form. See Relief for Late Elections.