Wednesday marks the sixth anniversary of the passage of the Affordable Care Act. Also known as Obamacare, the ACA has brought health coverage to an estimated 17 million people, but it has been a subject of controversy since before it was passed. As a result, the Supreme Court is spending the anniversary hearing the fourth challenge to the law in as many years, in a case called Zubik v. Burwell.

A consolidation of seven separate lawsuits, Zubik is essentially a continuation of the landmark 2014 Hobby Lobby v. Burwell case. The Hobby Lobby decision allowed private businesses with religious objections to opt out of the ACA's contraception coverage requirement by filing a notice with insurers or the federal government. The government would then offer such coverage to the companies' employees.

The latest challenge takes issue with the limited opt-out, or accommodation, for fertility treatments and contraception provided by the Hobby Lobby ruling. In Zubik, religious groups say that the act of filing a notice, while still allowing the coverage, imposes an unfair burden on them that violates their faith. At issue is whether the federal government has violated the 1993 Religious Freedom Restoration Act, which prevents the government from substantially burdening individuals of faith, unless it can prove a compelling interest. (David A. Zubik is the bishop for the Diocese of Pittsburgh.)

The challenge is particularly important because it's one of the first business cases to be heard, and potentially decided, with just eight justices, following the death of Antonin Scalia in February. The even number of justices, divided between four conservatives, three liberals, and the more centrist justice Anthony Kennedy, could lead to a split decision in the case, according to some legal experts. In 2014, the court's 5-4 decision in Hobby Lobby was divided along ideological lines.

Should the decision end in a draw, the ACA could mean different things in different states, depending on federal court of appeals rulings, legal experts say. So far, only the U.S. Court of Appeals for the 8th Circuit has ruled against the Obama administration on this particular issue. That court has jurisdiction over Arkansas, Iowa, Minnesota, Missouri, Nebraska, North Dakota, and South Dakota. Still, failing a clear Supreme Court opinion, other challenges could soon arise.

"This is territory that has never been trod on before, where you could have the Supreme Court ruling on the issue, but not providing [a clear legal direction]," says Steven Friedman, co-chair of the employee benefits practice at law firm Littler Mendelson, who adds the best practice for businesses is to continue complying with the ACA as hashed out under the Hobby Lobby ruling.