WASHINGTON — Republicans who control Congress said Wednesday they had struck a deal on legislation to overhaul the tax code, but they refused to release details amid reports tax rates would increase for corporations and drop for people with the highest incomes.

The legislation, which is still being finalized, would cut the top tax rate for the wealthy from 39.6% to 37%, lower the corporate income tax rate from 35% to 21% — an uptick from 20% that has been in earlier House and Senate plans — and allow homeowners to deduct interest only on the first $750,000 of a new mortgage, The Associated Press reported.

But Republicans refused to confirm details of the plan, and Democrats at a hearing convened to discuss it were told by the Republican chairman they could not see or even ask questions about the bill.

Sen. Orrin Hatch, R-Utah, chairman of the Senate Finance Committee confirmed an agreement had been reached between House and Senate leaders on a single bill that meshes competing tax plans that passed the House last month and the Senate in early December.

At Wednesday's meeting of a House-Senate conference committee — traditionally convened to work out differences between legislation passed by the two chambers — House Ways and Means Chairman Kevin Brady, R-Texas, told Democrats they would see the final bill when it was finished at the end of the week. Brady said the members could express their views on it when both chambers vote on it next week.

President Donald Trump promised tax cuts were on the way in a White House speech.

“As a candidate, I promised we would pass a massive tax cut for the everyday, working American families who are the backbone and the heartbeat of our country,” Trump said. “Now we're just days away.”

Trump said Internal Revenue Service has concluded that if a tax bill is signed by Christmas, the tax withheld from workers’ paychecks could be adjusted as soon as February.

Trump told reporters before a lunch with some members of the conference committee he would accept a top corporate rate or 21% in the bill. During last year's campaign, Trump had said he wanted a 15% corporate rate, but 21% would provide more revenue to settle other differences in the House and Senate bills.

The bills passed in both chambers with only Republican votes have hundreds of differences, including the top and lower rates, how many tax brackets there are, and when changes take effect or phase out. Under a budget framework both houses passed in October, the tax changes cannot add more than $1.5 trillion to the deficit over the coming decade.

Trump and congressional Republicans made a tax bill their top priority after failing to reach agreement in attempts to overhaul health insurance and repeal the Affordable Care Act, also known as Obamacare.

Democrats have voted unanimously against the tax bills. Senate Minority Leader Chuck Schumer D-N.Y., on Wednesday morning called for action on taxes to be delayed until the newly elected senator from Alabama, Democrat Doug Jones, can be sworn in.

“Senate Democrats are calling on Mitch McConnell to hit pause on the tax bill,” Schumer said.

Rep. Richard Neal, D-Mass., tried to postpone the hearing of the conference committee Wednesday afternoon until Jones could arrive.

Brady told him the committee's rules did not allow him to make that motion, an answer Brady repeated often as increasingly agitated Democrats tried to find out if the committee would meet again to consider the final tax bill (it won't), or whether there would be a formal "score" of the economic impacts of the final bill (that is expected, but Brady wouldn't say so).

Rep. Lloyd Doggett, D-Texas, said he sensed fear among the Republicans.

"It is the fear that if you don’t rush this through, with no questions, no amendments, no nothing, if the American people really find out what is in this bill, they will reject it and it will never be able to become law," Doggett said.

Republicans united behind the plan, saying that along with lower taxes on workers’ pay, the lower rates for businesses will generate a stronger economy with more jobs that pay higher salaries.

“We reject the idea that America cannot do any better than the status quo, which seems to be the attitude of our members across the aisle,” said Sen. John Cornyn, R-Texas.

Democrats argue that the true cost of the tax plan will come in the future, when increased deficits – official scorekeepers said it would add at at least $1 trillion to the national debt, even after economic growth is taken into account – prompt Republicans try to make cutbacks to Social Security, Medicare, education, and the social safety net.

“In America today, the very wealthy are becoming much more wealthy while the middle class continues to shrink, and your solution is to give 62% of the benefits to the top 1%?” said Sen. Bernie Sanders, I-Vt.

Rep. Don Young, R-Alaska, said Democrats should be happy Republicans were passing a bill as awful as the one they described, since they would be able to tell voters how the GOP hurt the country.

“If it doesn’t work, blame us,” Young said.

Sen. Bob Corker, a Republican from Tennessee who opposed the bill when it came up on Dec. 2, said passage was inevitable.

“There’s a locomotive,” Corker said. “It’s not stoppable.”

White House officials believe the tax plan’s benefits will put Democrats on the defensive in the midterm elections, especially those in states that Trump won in 2016.

“It will be very difficult for some Democratic senators particularly to go home after this passes and say, 'I had a chance to give you a lower tax bracket and expand the child care tax credit, double your standard deduction . . . But I said no,’” said White House counselor Kellyanne Conway.

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Contributing: Eliza Collins, David Jackson, Deirdre Shesgreen