WASHINGTON (AP) — Silena Davis had counted on an early tax refund to pay for getting her teeth fixed. Now, because Congress has dawdled all year on a tax bill, she and millions of other early filers could have to wait extra weeks for refunds that last year averaged $2,291.

The Internal Revenue Service is looking hard at delaying the start of its filing season, set to kick off on January 14, if Congress fails to pass legislation in the next two weeks. At issue is how to handle what could be a dramatic increase in the number of people facing a higher alternative minimum tax.

If there is a delay and it extends into mid-February, it would slow nearly 38 million refunds worth a total of about $87 billion, the IRS Oversight Board predicts.

"It would definitely make a big difference with me," said Davis, a George Washington University Law School administrator. "I'm going to have to get a crown and it's going to be really expensive."

The board, an independent advisory group, said in a report to lawmakers last week that it is "gravely concerned about the serious risks" to the filing season if Congress does not make timely changes to the tax. They include more mistakes by both taxpayers and the IRS and more people failing to pay taxes because of uncertainty about what they owe.

The alternative minimum tax was passed in 1969 and was aimed at about 155 very wealthy families who used deductions to avoid paying any federal income tax. The AMT disallows certain deductions and credits. It was not adjusted for inflation; as a result, over the years it has hit a growing number of middle-income taxpayers.

More than four million were subject to it in the 2006 tax year, and that could soar to 25 million this year without congressional action.

Congress in recent years has approved one-year fixes to stop the tax from expanding. Legislation this year has stalled in a dispute between majority Democrats and the White House. The stumbling block is whether some taxes should rise to offset the cost of correcting the AMT.

Richard Spires, the deputy IRS commissioner for operations support, said in an interview that the agency is considering not processing all early returns if the AMT issue is not resolved soon.

"We are worried that if we allow certain filers to file that it does not cause a lot of confusion and delay the whole filing system for everyone," he said.