(CNN) -

The biggest case of the Supreme Court's term involves a three-headed, hot-button appeal combining abortion rights, religious liberty, and the Affordable Care Act. It's also the last one, and a ruling is due on Monday.

The legal and social pique may not reach the heights of two years ago when the justices narrowly preserved the Affordable Care Act and its key funding provision in a blockbuster ruling.

But the stakes are still large, and the decision could serve as a primer for other pending challenges to the health law championed by President Barack Obama and in play as a campaign issue this midterm season.

The issue before the justices is whether the Affordable Care Act can mandate contraception coverage specifically for certain businesses that object for religious reasons.

"This case isn't that practically important, except for the employees and businesses involved. There just aren't a huge number of those," said Thomas Goldstein, publisher of SCOTUSblog.com and a Washington appellate attorney.

"But everyone can agree the social questions presented-- about when people can follow their religious convictions, and when people are entitled to contraception care-- are truly important," he said.

Hundreds of advocates and demonstrators representing both sides are expected to rally in front of the courthouse on Capitol Hill.

Contraception mandate

The section of law in dispute requires for-profit employers of a certain size to offer insurance benefits for birth control and other reproductive health services without a co-pay.

A number of companies equate some of the covered drugs, such as the so-called "morning-after" pill, as causing abortion.

The specific question presented was whether these companies can refuse, on the sincere claim it would violate their owners' long-established moral beliefs.

The First Amendment says that "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof."

"How does a corporation exercise religion?" asked Justice Sonia Sotomayor at March's oral arguments, summarizing perhaps the key constitutional question at hand.

"This is a religious question and it's a moral question," added Justice Samuel Alito, suggesting the businesses have such a right. "You want us to provide a definitive secular answer."

Conestoga, Hobby Lobby

The justices have a good deal of discretion to frame the competing issues and could reach a limited "compromise" through narrow statutory interpretation.

They could conclude individual owners can make the religious freedom claim, bypassing the corporate rights argument, but still give female workers the flexibility to get covered drugs.

The court weighed two related appeals from Conestoga Wood Specialties, a Pennsylvania cabinet maker, and Hobby Lobby, an Oklahoma-based retail giant that will have more than 700 arts-and-crafts stores nationwide by year's end.

Both corporations emphasized their desire to operate in harmony with biblical principles while competing in a secular marketplace. That includes their leaders' publicly stated opposition to abortion.

The case presented a complex mix of legal, regulatory, and constitutional concerns over such thorny issues as faith, abortion, corporate power, executive agency discretion, and congressional intent.

Health law impact

The political stakes are large, especially for the future effectiveness of the health law, which marks its fourth anniversary this year.

The botched rollout last fall of HealthCare.gov, the federal Affordable Care Act website, has become another political flashpoint along with other issues that many Republicans say proves the law is unworkable.

They have made the Affordable Care Act a key campaign issue in their fight to overtake the Senate, and retain control of the House.

Supporters of the law fear a high court setback on the contraception mandate will lead to other healthcare challenges on religion grounds, such as do-not-resuscitate orders and vaccine coverage. More broadly, many worry giving corporations religious freedom rights could affect laws on employment, safety, and civil rights.

The abortion link

The Hahn family, owners of Conestoga, and the Green family, owners of Hobby Lobby, said some of the mandated contraception prevent human embryos from being implanted in a woman's womb, which the plaintiffs equate with abortion.

That includes Plan B contraception, which some have called the "morning after" pill, and intrauterine devices or IUDs used by an estimated 2 million American women.

A key issue for the bench has been be interpreting a 1993 federal law requiring the government to seek the "least burdensome" and narrowly tailored means for any law that interferes with religious convictions.

Chief Justice John Roberts could be the "swing" vote as he was two years ago when siding with the court's more liberal members to allow the law's "individual mandate" to go into effect.