WASHINGTON — At least 18 million people would lose health insurance in the first year if Republicans re-create previous plans to repeal major portions of the Affordable Care Act, according to a report from the nonpartisan Congressional Budget Office.

The number of people without insurance would grow to about 32 million within the first decade if Congressional Republicans follow a 2015 plan to repeal the health-care law without a replacement, the new report says. It also estimates that health insurance premiums for people buying individual non-group coverage would go up by about 50 percent in a decade, further complicating Republican promises that people will not lose coverage under their plan.

The report comes as Republican leaders in Washington are working furiously to tamp down concerns within their ranks that a speedy push to repeal major portions of the Affordable Care Act could create chaos in the insurance markets and provoke backlash from voters. Last weekend, President-elect Donald Trump promised in an interview with The Washington Post that he was nearing completion of a plan to provide “insurance for everybody.” Trump did not provide any details of what that plan would include.

The new report sparked bickering among lawmakers Tuesday as Republicans dismissed the report, arguing that the forthcoming Republican repeal plan will also include some elements of replacement.

“This projection is meaningless, as it takes into account no measures to replace the law nor actions that the incoming administration will take to revitalize the individual market that has been decimated by Obamacare,” said AshLee Strong, a spokeswoman for House Speaker Paul Ryan, R-Wis.

Senate Democrats, including Senate Minority Leader Charles Schumer, D-N.Y., requested the report to provide an updated estimate of the impact of a 2015 repeal measure that ended in a veto from President Barack Obama. Republican leaders have said that they plan to closely model an upcoming repeal measure on that 2015 legislation and conservative groups have openly touted that bill as a “dress rehearsal.”

“Nonpartisan statistics don’t lie: it’s crystal clear that the Republican effort to repeal the Affordable Care Act will increase health care costs for millions of Americans and kick millions more off of their health insurance,” Schumer said in a statement.”

But Republicans insist that they are working on a replacement plan. House Minority Whip Steve Scalise, R-La., the third ranking Republican in the House, responded Tuesday by dismissing the report on Twitter.

“The CBO report assumes no Obamacare replacement. In reality, we will provide people with coverage that they want and can actually use,” he posted.

Congress took its first step toward rolling back Obama’s health-care reform law Friday when House voting along party lines to pass a budget measure that paves the way for a repeal vote in the coming months. Committees in the House and Senate are set to begin writing legislation that will roll back major elements of the health care law, including penalties for those who don’t get insurance and credits that help people buy insurance on the private market.

Republicans are now facing the far more difficult difficult task of assembling a viable replacement for a law that has expanded health insurance coverage to roughly 20 million Americans and eliminated unpopular insurance industry practices, such as lifetime coverage caps and widespread refusal to cover already-sick individuals.

The Washington Post’s Mike DeBonis contributed to this report.