If you’re one of the ambitious few who line up to file their returns at the opening bell of tax season, you might want to do a little AMT research first.

As many as 13.5 million taxpayers might be impacted by recent legislation that provides a year’s worth of relief from the alternative minimum tax. That legislation has forced the IRS to reprogram five AMT-related tax forms, a time-consuming process that will force those 13.5 million taxpayers to wait until Feb. 11 to file their returns.

The vast majority of taxpayers will, as usual, be able to file their returns starting in early January.

“We regret the inconvenience the delay will mean for millions of early tax filers, especially those expecting a refund,” said acting IRS Commissioner Linda Stiff. “We’ve taken extraordinary steps to figure out a way that we can start the filing season on time for most taxpayers, including some using AMT-related forms. Our goal has always been to make sure we can accurately process tax returns while getting refunds to taxpayers as quickly as possible.”