After years of vowing to repeal—and then to repeal and (reluctantly) replace—former President Barack Obama’s signature health care law, House Republicans unveiled their own plan Monday. The GOP version of Obamacare gets rid of the individual mandate requiring individuals to have health insurance, but keeps popular provisions that disallow insurers from denying coverage based on pre-existing conditions and allow young adults up to the age of 26 to stay on their parents’ health plans.

The Republican plan aims to replace the individual mandate with a series of incentives to coax individuals to sign up for coverage rather than being penalized for failing to sign up, as is the case under Obamacare. The reasoning behind the individual mandate, and the Republican alternative, is to increase the coverage pool and to include younger, healthier individuals in the coverage scheme.

Under GOP bill, anyone who goes w/o health coverage for two months or more would face a 30% surcharge on premiums for a year. pic.twitter.com/krmLYLTOTn — Kyle Cheney (@kyledcheney) March 6, 2017

“Republicans hope to undo major parts of President Barack Obama’s signature domestic achievement, including income-based tax credits that help millions of Americans afford insurance, taxes on people with high incomes and the penalty for people who do not buy health coverage,” according to the New York Times. “Under the Republican plan, the income-based tax credits would be replaced with credits that would rise with age. In a late change, the plan was also expected to include language limiting who is eligible for the tax credits, so that affluent Americans would not receive them.” There are concerns, however, that without income-based tax credits the cost of coverage will quickly exceed what lower- and middle-income families can afford.

The introduction of the Republican plan appears to be just the beginning of what looks likely to be a contentious process of trying to upend the 2010 Affordable Care Act, which, despite the vitriol, does have many features that Americans not only like, but have come to rely on. Also, after six years of railing against Obamacare, the GOP plan does not include a price tag or an estimate of how many Americans the plan will actually cover. That makes it pretty hard to assess in any real way. “Even so, signs emerged on Monday that Republicans in Congress’s upper chamber could balk if the legislation leaves swaths of the country without insurance coverage,” the Washington Post reports. “Four key Republican senators said they would oppose any new plan that would leave millions of Americans uninsured … With 52 Republicans, [Majority Leader Mitch] McConnell would not have enough votes to pass repeal without the support of at least two of those senators.”