Medicaid isn’t the only healthcare program that’s in for an overhaul under the Republican Party’s “one big, beautiful bill.”

The controversial tax and spending package, which passed the House Thursday with the help of pressure from President Trump, also includes several reforms to the Affordable Care Act that are expected to shrink the number of Americans who obtain insurance through the law’s marketplaces.

The legislation would end the option to automatically renew coverage each year and make signing up outside of the normal open enrollment period more difficult, adding red tape that some health experts say could end up blocking Americans from coverage they would otherwise qualify for.

It would also require people to return more money to the government if they receive overpayments on their insurance subsidies. As a result, many Americans could unexpectedly find themselves on the hook for thousands of dollars when they file taxes.

“Each one of the provisions sounds maybe a little wonky or technical,” said Cynthia Cox, director of the Program on the ACA at the healthcare think tank KFF. “But when you put it all together, especially when you think about all the interaction between them, it could make it much harder to sign up for coverage.”

The changes to Obamacare will leave about 4 million fewer Americans insured, according to estimates by the Congressional Budget Office. They are also coming on top of cuts to the law’s subsidies already scheduled for 2026, which were expected to knock more than 4 million people off its rolls.

About 24 million Americans signed up for coverage on the ACA’s exchanges this year.

Claims of fraud

Conservatives argue that the reforms are needed to fight what they describe as rampant fraud on Obamacare’s exchanges, driven in part by insurance brokers who use bogus sign-ups in order to earn commissions.

They point out that tens of thousands of Americans have complained about being enrolled in coverage or switched between plans without their permission in recent years. Federal investigators have also uncovered cases of brokers encouraging clients to lie about their finances in order to qualify for subsidized insurance.

For instance, according to Department of Justice prosecutors, last month one executive pleaded guilty to running a $133 million scheme in which “street marketers” rounded up and bribed “individuals experiencing homelessness, unemployment, and mental health and substance abuse disorders” to fraudulently sign up for subsidized ACA coverage when they lacked the minimum income.

Those schemes reflect a quirk in how Obamacare works. Under the program, Americans only qualify for premium tax credits if their earnings put them over the poverty line, since the law’s authors had wanted lower-income households to use Medicaid.