As the Sept. 17 deadline approaches for calendar year filers of corporate returns who filed for extensions, the Internal Revenue ServiceĀ is urging corporate filers to be aware of their obligation to file electronically. The requirement to e-file now covers all corporations with assets over $10 million that file 250 or more returns, such as Forms W-2 and 1099, annually. Last year, the requirement started for certain large corporations, those with assets over $50 million.Ā About 15,000 large corporations e-filed last year. So far this year, 8,000 large corporations have e-filed.