(Reuters) – U.S. Republican senators are leaning towards a plan to delay the effective date of an Obamacare repeal for three years, a senior Republican has said.

But some conservatives in the House of Representatives think that is too long to wait for the end of the Affordable Care Act, as President Barack Obama’s signature health insurance program is known.

“In the Senate, there’s consensus for three years,” Senator Orrin Hatch, chairman of the chamber’s finance committee, told reporters, saying it could take that long to work out a replacement for Obamacare. “It takes time to do things around here.”

Republicans in both the House and Senate say they want to repeal Obamacare early in 2017; it will be the first order of business in the Senate in January, Senate Majority Leader Mitch McConnell, a Republican, has said.

Donald Trump’s election as U.S. president last month means Republicans will control the White House, Senate and House of Representatives in 2017. The new Congress goes to work on Jan. 3; Trump will be sworn in on Jan. 20.

But Republicans have not agreed on how quickly the Obamacare repeal should go into effect. A delay would give them time to work on a replacement, instead of throwing millions of Americans out of their health insurance with no substitute.

Some House conservatives favor phasing out Obamacare and getting a replacement within two years, because three years would not lapse until after the next congressional election, with the attendant uncertainty about who will be in the majority then.

“We don’t think it’s very wise to leave a long-term plan like that up to a (future) Congress that you can’t necessarily control,” said Ben Williamson, spokesman for Representative Mark Meadows, the incoming leader of the Freedom Caucus, a group of about 40 House conservatives.

“There is a potential that some members of the Freedom Caucus might vote against repeal, if the replacement was going beyond two years,” Williamson said.

The Affordable Care Act has provided some 25 million previously uninsured Americans with health coverage. Republicans have repeatedly tried to dismantle the law, which they call a government overreach. Another senior senator said some Republicans are worried about whether they will have to raise taxes in three years to pay for an Obamacare replacement, which could for example involve tax credits to subsidize health insurance.

“What Republicans could be faced with in three years, is voting for a tax increase . . . and that’s not exactly a place that Republicans relish being,” said Senator Bob Corker, chairman of the Senate Foreign Relations committee.