The Supreme Court appeared divided Monday over the constitutionality of a government task force that determines what preventive health care services insurers must cover at no cost under the Affordable Care Act of 2010.

Tens of millions of Americans have benefitted from the group's binding recommendations to health plans, which must underwrite a broad range of treatments from cancer screenings to cholesterol-lowering medications and drugs to prevent the spread of HIV.

A group of Christian-owned businesses is challenging the arrangement, alleging that the U.S. Preventive Services Task Force, which operates out of the Department of Health and Human Services, is not legally structured and possesses unchecked power to influence the health care system. Lower federal courts agreed.

The 16-member panel of expert volunteers is appointed by the HHS secretary. Members are removable at-will, but they are not confirmed by the Senate. It is also supposed to operate "independent" of political influence, meaning its recommendations are not directly reviewable.

The Trump administration, which is defending the task force, argues members are supervised by the HHS secretary, who is Senate-confirmed and can effectively override any of the group's decisions.

The Court's three liberal members -- Justices Sonia Sotomayor, Elena Kagan and Ketanji Brown Jackson -- all appeared inclined to uphold the task force's authority and the recommendations for covered preventive services since 2010.

Justices Brett Kavanaugh and Amy Coney Barrett also seemed open to affirm the arrangement under the landmark health law, but their positions were not entirely clear.

At one point, Kavanaugh notably suggested the task force was not as independent or powerful as critics are making it out to be.

"Your theory depends on us treating the task force as this massively important agency that operates with unreviewable authority to make really critical decisions that are going to affect the economy and without any supervision or direction by the secretary," Kavanaugh told Jonathan Mitchell, the attorney representing the Christian businesses. "Normally, before that kind of thing would happen, Congress would have provided stronger indications that this task force is enormously important in the American economy and would have treated it such. And I just don't see indications of that."

Justices Samuel Alito, Clarence Thomas and Neil Gorsuch appeared more sympathetic to the challengers.

"What's the statutory authority to appoint the task force?" Thomas asked Deputy Solicitor General Hashim Mooppan.

Mooppan replied, citing a federal law that allows an HHS direct to "convene" a task force. Thomas suggested Congress never designated anyone the authority to run the group.

"You're using the word 'convene,'" he said. "I think that normally connotes just calling a meeting or something. The court was convened this morning. The chief [justice] didn't appoint any of us."

For his part, Chief Justice John Roberts -- who famously has voted to save the Affordable Care Act from existential challenges in the last 15 years -- remained relatively quiet during the debate.

Among the services implicated in the case are no-cost coverage for statins to lower cholesterol; colonoscopies for 45- to 49-year-olds; preexposure prophylaxis (PrEP) medicine to reduce the spread of HIV; medications to lower the risk of breast cancer for women; and lung cancer screenings for smokers.

If the justices uphold lower court rulings that the task force is unconstitutional, its recommendations since 2010 could be invalidated -- and along with them the guarantee of no-cost preventive services coverage many people enjoy.

"The case is not the kind of existential threat that we have seen in previous Supreme Court cases involving the ACA, but it's certainly something that could affect a lot of people," said Larry Levitt, executive vice president at KFF, a nonpartisan health policy group.

The heart of the legal dispute turns on the Constitution's Appointments Clause. The provision requires "principle officers" of the U.S. government, such as Cabinet secretaries and ambassadors, to be confirmed by the Senate. It stipulates that "inferior officers" who are appointed by Senate-confirmed officials are permissible, provided they are supervised and reviewed.

The plaintiffs allege that members of the task force not properly appointed since they are not Senate-confirmed. The Trump administration insists they are "inferior officers" of the government and not subject to the confirmation requirement.

“Americans have the constitutionally protected freedom to live and work according to their religious beliefs, and governments exist to defend that freedom," said Daniel Grabowski, an attorney with Alliance Defending Freedom, a conservative legal advocacy group supporting the plaintiffs. "We urge the Supreme Court to restore this accountability within the federal government and to the American people.”

More than 150 million Americans rely on early screenings and interventions for chronic conditions under no-cost preventive services, according to American medical organizations. Public health groups say a decision striking down the task force could deeply affect the long-term health of Americans and disease prevention efforts. Insurers worry that it could inject instability into the insurance market, while hospital groups fear they may have to shoulder more of the burden from people who are sicker.

"The ACA’s preventive services requirement has been a game-changer, providing access to evidence-based preventive care and early detection of serious medical conditions," said Wayne Turner, a senior attorney at the National Health Law Program, a nonprofit group that advocates for low-income communities. "The ACA’s coverage and cost-sharing protections are especially important for low-income persons, who will be harmed most if the Supreme Court refuses to allow the ACA provision to stand."

A decision in the case -- Kennedy v. Braidwood Management -- is expected by the end of June.