Cherry blossoms, daffodils, and the first breath of spring can mean only one thing in the nation's capital: another Affordable Care Act case before the Supreme Court.

The act made its fourth trip to the top court Wednesday, with the justices' ideological split as evident as ever in their sharply worded questions.

The death of Justice Antonin Scalia weighed heavily on the 90-minute session, as it reduced the conservative contingent to four justices and increased the odds of a 4-4 tie. That would leave the case without a clear resolution and raise the possibility of a rehearing when a new justice joins the court.

The challengers in Zubik v. Burwell object to a government rule that lets religious groups opt out of the ACA's mandate that insurance plans cover contraceptives without cost sharing. Houses of worship are entirely exempt from the mandate, but religiously affiliated charities, like hospitals and universities, must submit a form that triggers coverage directly through their insurance plan.

The more than two dozen religious groups challenging the rule, most of them Catholic charities, contend that it entangles them in providing contraceptive coverage, which violates their religious beliefs. If they try to avoid the rule by declining to provide health coverage altogether, they face the prospect of big fines.

Three of the conservative justices seemed to agree. Chief Justice John G. Roberts Jr., who had cast swing votes backing the government in two past ACA cases, asked Solicitor General Donald Verrilli to explain how the rule does not make religious groups complicit in providing contraceptive coverage.

"The petitioners use the phrase hijacking, and it seems to me that's an accurate description of what the government wants to do," Roberts said.

Justice Samuel A. Alito Jr. asked why an alternative to the accommodation could not have been crafted, such as offering separate, contraceptive-only policies on the ACA's insurance exchanges, which would impose less of a burden on the challengers' beliefs.

Justice Anthony M. Kennedy, who cast a swing vote in favor of the government in last year's ACA case challenging some insurance premium subsidies, was also skeptical of the government's position. "Do you question their belief that they are complicit in the moral wrong?" he asked. "Then it seems to me that that's a substantial burden on their religious beliefs."

Justice Clarence Thomas, who broke his decadelong silence last month, reverted to it Wednesday but is likely to back the conservatives.

The four liberals were equally forceful in questioning the lawyers for the religious groups. Justice Elena Kagan asked attorney Paul D. Clement if the challengers were really "objecting to objecting" to the contraceptive mandate, which, if upheld, could open the door to a flood of noncompliance with government programs.

Justice Sonia Sotomayor asked, if broad religious objections are permitted to government actions, "how do we ever have a government that even functions?"

Justice Stephen G. Breyer said that religious people who are members of society must often do things they find objectionable.

Justice Ruth Bader Ginsburg feared that the challengers' arguments could open the floodgates to permit exemptions for everyone. Unlike two of the last three ACA cases, this one does not challenge any of the law's core provisions. A ruling adverse to the government would leave the law largely in place, but with fewer employers offering no-cost coverage for contraceptives.

The case has aroused strong feelings on both sides. Carol Tracy, executive director of Philadelphia's Women's Law Project, said, "Reproductive health is central to women's health care. Unnecessary riders are burdensome and punitive. Contraception should be paid for in the same way as other health services."

Edward J. Furton, ethicist at the National Catholic Bioethics Center in Philadelphia, called the government's accommodation for religious groups "a bit of a shell game." "Religious organizations are still initiating the actions which bring about the coverage. The accommodation shows disregard for common sense and respect for religious liberty."

A tie among the justices would mean prior rulings on the case by federal appeals courts would remain in place. Those rulings have upheld the accommodation in seven federal circuits, leaving it to take effect in the areas they govern, and struck it down in one.

However, the court could issue a stay on enforcement of the rule in all regions pending a rehearing before a full complement of nine justices.