A requirement under the U.S. law known as Obamacare that private insurance plans cover drugs that prevent HIV infection at no cost to patients violates both federal law and the Constitution, a federal judge ruled on Wednesday, siding with conservative lawyers who had challenged the measure on religious grounds.

Ruling in Fort Worth, Texas, U.S. District Judge Reed O'Connor found that the HIV pre-exposure prophylaxis, or PrEP, mandate stemmed from a recommendation by an advisory body formed in violation of constitutional requirements and could infringe upon the rights of employers under a law called the Religious Freedom Restoration Act. The mandate is part of the Affordable Care Act (ACA), as Obamacare is formally called.

The legal challenge was filed in 2020 by eight individuals and two businesses, all from Texas. They argued that the free PrEP requirement, as well as free coverage requirements for contraceptives and the human papillomavirus (HPV) vaccine, requires business owners to pay for services that "encourage homosexual behavior, prostitution, sexual promiscuity and intravenous drug use" despite their religious beliefs.

The conservative America First Legal Foundation is helping to represent the plaintiffs. The group was founded by Stephen Miller, who served as an adviser to Republican former President Donald Trump.

The American Cancer Society Cancer Action Network said in a statement that the ruling could threaten free preventive care more broadly, including routine cancer screenings.

O'Connor, an appointee of Republican former President George W. Bush, ruled in 2018 in a previous case that the ACA, a landmark U.S. healthcare law signed by Democratic former President Barack Obama in 2010, was unconstitutional.

The Supreme Court subsequently ruled in 2021 that Texas and other states that had challenged Obamacare with the support of Trump's administration lacked the proper legal standing to pursue that case. The ACA has survived several reviews by the U.S. Supreme Court.

O'Connor has not yet specified how his new ruling will be enforced. It is not clear what the judge's decision means for the advisory body, called the Preventive Services Task Force (PSTF), which is convened by an official of the U.S. Department of Health and Human Services (HHS) and recommends a wide range of preventive services to be covered under the ACA.

The judge found that the U.S. Constitution requires that the task force's members be appointed directly by the president.

O'Connor has not yet ruled on the challenge to the contraceptives mandate and rejected the challenge to the HPV vaccine mandate. The HPV vaccine sold by Merck & Co prevents cancers caused by the virus.

HHS said in a statement that it "continues to work to ensure that people can access healthcare, free from discrimination."

A lawyer for the plaintiffs had no immediate comment.

The PrEP drugs approved in the United States to prevent HIV infection, which can cause AIDS, are made by Gilead Sciences Inc and by ViiV Healthcare, a joint venture of GSK Plc, Pfizer Inc and Shionogi & Co Ltd.

A GSK spokesperson said PrEP coverage was "critical to ensuring health equity and helping end the HIV epidemic" and that the company would follow the case as it develops.