WASHINGTON (AP) — A federal judge heard arguments Wednesday in a lawsuit that poses a threat to the nationwide availability of a popular abortion medication. The hearing comes as a conservative Christian group seeks to reverse federal approval of the drug mifepristone.

A two-pill combination of mifepristone and another drug is the most common form of abortion in the U.S. and the ruling would affect states where abortion is legal as well as those that outlaw it. The case has raised concerns about court transparency and so-called judge shopping.

Here's a look at some of the legal issues surrounding the case:

HOW DID IT START?

Abortion opponents who helped overturn Roe v. Wade filed a lawsuit in November, asking a judge in Texas to reverse the approval of mifepristone.

Research shows that medication-induced abortions are safe and effective, and they were approved by the Food and Drug Administration more than 20 years ago.

But the group, Alliance Defending Freedom, argued in the lawsuit that the FDA process was flawed for mifepristone. It also took aim at more recent changes that have eased access to the drug.

The suit was filed in Amarillo, Texas, which meant that it was assigned to U.S. District Judge Matthew Kacsmaryk, a former attorney at a Christian law firm who previously wrote critically about Roe. He was appointed by former President Donald Trump and confirmed over fierce opposition from Democrats.

WHY IS IT IMPORTANT?

Medication is the most common form of abortion in the U.S., according to the Guttmacher Institute, a research group that supports abortion rights. It's become more available as the FDA allowed it to be prescribed online and sent through the mail. Demand continued as states began banning abortion after Roe was overturned and more women traveled for access, or sought medication online.

If Kacsmaryk reverses the approval of mifepristone, it could restrict access nationwide. Such a ruling would be an unprecedented challenge to the FDA, which approved mifepristone in combination with a second pill, misoprostol, as a safe and effective method for ending a pregnancy in 2000.

That would be "nothing short of catastrophic," a group of 22 Democratic-led states said in court documents filed in the case. Another group of 22 Republican states filed briefs supporting the reversal. They argue the ability to order pills by mail undermines their laws banning abortion.

WHY IS THIS IN THE HANDS OF ONE TEXAS JUDGE?

Kacsmaryk is a federal judge and one of the major tasks of the U.S. court system has always been deciding whether laws and policy are constitutional. That means any judge weighing a case challenging a federal law or policy could make a decision that has ripple effects across the nation.

Lawyers on either side of a case can appeal a ruling, however, and federal appeals courts can block or overturn a decision. In this case, an appeal would go to the 5th Circuit Court of Appeals, which also leans conservative. It upheld Kacsmaryk's decision in another high-profile case requiring the Biden administration to continue the "Remain in Mexico" immigration policy implemented by Trump. The ruling was later overturned by the Supreme Court.

The case has also raised concerns about judge shopping, a term for litigants seeking to file cases in front of judges they consider sympathetic to their cause. It's a tactic that's been utilized by groups across the ideological spectrum, but the volume of cases filed before Kacsmaryk and other Texas judges has raised concerns among experts.

WHAT SET OFF TRANSPARENCY ALARM BELLS?

Kacsmaryk set the first hearing in the closely watched case on a conference call with attorneys. He also asked them to for the "courtesy" of not publicizing the upcoming arguments, according to a court transcript.

He said he planned to delay making the hearing public until the evening before, making it difficult for many to attend because Amarillo is hours away from major cities. Such a delay is highly unusual in the American judicial system, where hearing notices are typically quickly made public and often scheduled weeks or months in advance.

After news reports about the call, the hearing was placed on the public docket a day and a half before it was scheduled.

WHAT HAPPENS NEXT?

A ruling in the case could come any time after the arguments conclude. A decision against the FDA would almost certainly be swiftly appealed by the Justice Department.

A ruling reversing approval 20 years later is all but unprecedented, so it's not clear exactly what would happen next or how quickly access might be curtailed. If mifepristone is sidelined, clinics and doctors that prescribe the combination say they would switch to using only misoprostol, the other drug in the two-drug combination, an approach that is slightly less effective.