Other no-cost services, including HIV screenings, are also impacted under the ruling by U.S. District Judge Reed O’Connor that opponents say will jeopardize preventive care for millions of Americans.

Experts cautioned that insurers are unlikely to stop any coverage immediately. The Biden administration was expected to appeal and seek a stay of the ruling.

“This is not the potential fatal blow to the ACA like previous court cases, but it would limit a very popular benefit that tens of millions of people use,” said Larry Levitt, executive vice president for health policy at the Kaiser Family Foundation.

The decision comes more than four years after O’Connor, a nominee of former President George W. Bush, ruled that the entire health care law also known as “Obamacare” was unconstitutional. The U.S. Supreme Court overturned that ruling.

This time O’Conner blocked only the requirement that most insurers cover a range of preventive care — including screenings for multiple types of cancer — siding with plaintiffs who include a conservative activist in Texas and a Christian dentist who opposed mandatory coverage for contraception and an HIV prevention treatment on religious grounds.

The requirements for coverage are driven by recommendations by the U.S. Preventive Services Task Force, which is made up of volunteers. O’Connor ruled that enforcing the recommendations was “unlawful” and a violation of the Constitution’s Appointment Clause, which lays out how government officials can be appointed.

Dr. Michael Barry, chairman of the federal task force, said in a statement following the ruling that people with low incomes have been able to get services they need as care has expanded over the past decade because of the law.

“Fundamentally, people across the country deserve the opportunity to receive these important preventive services that have been proven to help them live longer and healthier lives,” Barry said.

White House Press Secretary Karine Jean-Pierre said the Department of Justice and the Department of Health and Human Services were reviewing the ruling, but called the case “yet another attack” on the health care law that has been in place for 13 years and survived multiple legal challenges.

The Biden administration previously told the court that the outcome of the case “could create extraordinary upheaval in the United States’ public health system.” More than 20 states, mostly controlled by Democrats, had urged O’Connor against a sweeping ruling that would do away with the preventive care coverage requirement entirely.

The ruling applies to recommendations made by the task force after March 2010, when the Affordable Care Act was enacted. Some of the nation’s largest medical groups came out against the lawsuit, warning that insurers in the future could impose cost-sharing on patients for screenings that are now fully covered.

Levitt said if O’Connor’s ruling is allowed to stand, insurers are likely to look at changes in coverage beginning in the next calendar year, since existing contracts are already in effect.

Although the ruling impacts a broad spectrum of preventive care, it does not wipe out coverage for all preventive screenings. For instance, experts said the decision would not overturn coverage for preventive women’s health services that were approved outside the task force.

Some cancer screenings approved before 2010 would also not be affected, including screenings for cervical and colorectal cancer, said Alina Salganicoff, senior vice president and director for women’s health policy at the Kaiser foundation. But she said screenings for lung and skin cancer, which were more recently approved, could be affected.

In September, O’Connor ruled that required coverage of the HIV prevention treatment known as PrEP, which is a pill taken daily to prevent infection, violated the plaintiffs’ religious beliefs. That decision also undercut the broader system that determines which preventive drugs are covered in the U.S., ruling that a federal task force that recommends coverage of preventive treatments is unconstitutional.

Employers’ religious objections have been a sticking point in past challenges to former President Barack Obama’s health care law, including over contraception.

The lawsuit is among the attempts by conservatives to chip away at the Affordable Care Act — or wipe it out entirely — since it was signed into law in 2010. The attorney who filed the suit was an architect of the Texas abortion law that was the nation’s strictest before the Supreme Court overturned Roe v. Wade in June and allowed states to ban the procedure.