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A Texas judge who previously ruled that ObamaCare was unconstitutional has struck down a narrower but essential part of the law Thursday in a decision the Biden administration says could upend the U.S. health care system. 

Four years ago, U.S. District Judge Reed O'Connor found that ObamaCare, officially known as the Affordable Care Act, was unconstitutional in response to a challenge from 19 states led by Texas. The Supreme Court later overturned that decision. 

Now, Connor has ruled against the law again in a case concerning a conservative activist in Texas and a Christian dentist who claim that mandatory coverage for contraception and an HIV prevention treatment violate their religious conscience. 

The judge blocked the government's requirement that most insurers cover certain preventative care, writing in his opinion that recommendations for preventive care by the U.S. Preventive Services Task Force were "unlawful."

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The healthcare.gov website is seen on Dec. 14, 2021, in Fort Washington, Md.

The healthcare.gov website is seen on Dec. 14, 2021, in Fort Washington, Md. A federal judge in Texas who previously ruled to dismantle the Affordable Care Act struck down a narrower but key part of the nation's health law Thursday, March 30, 2023, in a decision that opponents say could jeopardize preventive screenings for millions of Americans. (AP Photo/Alex Brandon, File)

In court filings, the Biden administration had argued that blocking such recommendations "could create extraordinary upheaval in the United States’ public health system." It is expected to appeal O'Connor's ruling. 

"Preventive care is an essential part of health care: it saves lives, saves families money, and improves our nation’s health. Because of the Affordable Care Act’s preventive services requirement, 150 million Americans have access to crucial, free preventive care like cancer and heart disease screenings. Actions that strip away this decade-old protection are backwards and wrong," said Kamara Jones, a spokesperson for the Department of Health and Human Services. 

"HHS is currently reviewing the decision and consulting with the Department of Justice on next steps in the litigation. We will do everything we can to protect and defend Americans’ rights to the health care they need and deserve," Jones added. 

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Birth control pills

U.S. District Judge Reed O'Connor ruled Thursday that certain Obamacare mandatory insurance coverage requirements are unlawful, including coverage for contraception. Pictured: Birth control pills displayed in this illustration picture taken in Philadelphia, Pennsylvania, U.S., July 11, 2022. (REUTERS/Eduardo Munoz/File Photo)

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.

ObamaCare has faced several challenges on religious grounds before, including a lawsuit by the Little Sisters of the Poor, a group of Catholic nuns who objected to providing insurance coverage for contraception to its employees. The Supreme Court in 2020 upheld action by the Trump administration to expand exemptions to ObamaCare's insurance requirements that allowed religiously-affiliated groups and some for-profit companies to opt-out of the requirement. 

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Barack Obama

Former U.S. President Barack Obama signed the Affordable Care Act, also known as ObamaCare, into law in 2010 and Republicans have been trying to kill the law ever since, so far unsuccessfully.  (Reuters)

The Biden administration and 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.

"Over the last decade, millions of Americans have relied on the preventive services provisions to obtain no-cost preventive care, improving not only their own health and welfare, but public health outcomes more broadly," the states argued in a court filing.

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The lawsuit is the latest attempt by conservatives to undermine ObamaCare since the law was enacted in 2010. The attorney leading the lawsuit is John F. Mitchell, who is credited with inventing the novel enforcement mechanism of Texas' "feteal heartbeat" abortion ban, which was among the strongest pro-life laws in the nation before the Supreme Court overturned Roe v. Wade, permitting states to ban the procedure.

The Associated Press contributed to this report.