Delta Air Lines said it will refund federal ticket taxes paid by travelers who booked tickets before the Federal Aviation Administration partial shutdown started July 23 and who travel during the shutdown.

But the airline has made no move to rescind fare increases put in place after the tax collection stopped.

Delta and other airlines boosted fares after the shutdown, holding prices essentially steady and pocketing the extra revenue. That has drawn flak from some in Congress, and on Monday Transportation Secretary Ray LaHood said, "I don't think that's right or fair for airlines to do that.... That money is going directly into the coffers of airlines and costing passengers something that they shouldn't or don't have to pay."

A Congressional stalemate led to the FAA partial shutdown and the halt of the airline ticket taxes, which amount to more than 7.5 percent of the base fare. The Internal Revenue Service said passengers who paid for tickets -- and thus paid for the tax -- before July 23  and travel during the shutdown "may be entitled to a refund of the tax."

Although travelers pay the tax to airlines when they pay for tickets, the tax is based on the date of travel.

Delta on Monday said it is still awaiting guidelines from the IRS on how the process will work and that it will process refunds once an agreement is reached with the IRS.