The White House says the House of Representatives will vote Friday morning on overhauling Obamacare, as Republicans strive to find more "yes" votes.
A vote set for Thursday night was postponed when House leaders determined there were not enough votes to pass it.
Every Democrat is expected to vote no, while dozens of moderate and conservative Republicans say they will vote against it or are leaning that way.
Members of the House conservative bloc known as the Freedom Caucus said after meeting with President Donald Trump that they have reached no agreement on whether to support the Obamacare overhaul.
Congressman Mark Meadows, chairman of the Freedom Caucus, confirmed that his group and the president have not reached an agreement on the issue.
But the White House had a different interpretation of Trump's talks with the congressional conservatives. It released a statement saying the two sides had taken "a positive step" toward approving the proposed health care law.
White House spokesman Sean Spicer told reporters "many members" have indicated they will vote for the measure. But, he said, "at the end of the day, we can't make people vote."
"It's a balancing act," Spicer said.
The Affordable Care Act is one of former President Barack Obama's proudest achievements.
Obama weighs in
Obama released a statement Thursday urging lawmakers not to make changes that would fail to improve health care for all Americans.
"If Republicans are serious about lowering costs while expanding coverage to those who need it, and if they're prepared to work with Democrats and objective evaluators in finding solutions that accomplish those goals; that's something we should all welcome," Obama said.
"But we should start from the baseline that any changes will make our health care system better, not worse, for hardworking Americans. That should always be our priority."
Although Republicans hold a majority in both houses of Congress, passing the bill is far from certain because of opposition from conservatives who say it does not go far enough and moderates who fear too many Americans would lose insurance coverage.
'Loss is not acceptable'
Earlier this week, Trump warned of political retribution against members of the House who do not vote to overturn the health care law and send it on to the Senate, where its fate also is uncertain.
He said not following through on promises to overturn the Obama law could anger constituents and cost lawmakers their seats in the 2018 congressional elections.
"I'm going to come after you, but I know I won't have to, because I know you'll vote yes," Trump told Meadows. "Honestly, a loss is not acceptable, folks."
Trump and Republicans have long railed against Obamacare. The law added 20 million Americans to insurance rolls. But Republicans contend the cost of premiums and individual medical procedures not covered by the insurance have risen so much that many Americans can no longer afford to pay for the care they need.
The independent Congressional Budget Office last week concluded that 24 million Americans would lose health care coverage over the next decade if the Republican plan was approved. Trump and Republican leaders contend their plan, unlike Obamacare, will give people access to buy the coverage that meets their needs and that they can afford.
The Republican plan also cancels penalties that people would pay if they decide not to buy health insurance.
But the Trump plan keeps two popular Obamacare provisions — barring insurance companies from denying coverage to people with pre-existing medical conditions, and letting young people remain on their parents' policies until they turn 26.
House Speaker Paul Ryan said he remains confident he will have enough votes to approve the overhaul.
"This is the one chance we have to actually repeal Obamacare and replace it with the stuff we believe in," Ryan said. "The president is all in, we all made this promise, and that's why I'm confident. People will realize, 'I'm not going to go home and face voters reneging on my word.' "