A federal appeals court is hearing arguments on Wednesday in a case that could determine the availability of a medication used in a majority of abortions in the country.

A three-judge panel from the U.S. Court of Appeals for the Fifth Circuit is considering whether to uphold a preliminary ruling from a federal judge in Texas, who in April declared invalid the Food and Drug Administration’s 23-year-old approval of the pill, mifepristone.

Although the case is still in its early stages and any decision is likely to be appealed, it could ultimately have profound implications.

If the initial judge’s ruling is upheld, access to medication abortion would be upended in states where abortion is legal, not just in states where bans and restrictions are in force. The F.D.A.’s regulatory authority over other drugs could be challenged with other lawsuits, and pharmaceutical companies say that uncertainty about the F.D.A.’s role could chill drug development in the United States.

The arguments included whether the parties who brought the suit — a coalition of organizations and doctors who oppose abortion and do not prescribe the pill — could show they would suffer real harm if the medication continued to be available and whether they waited too long to challenge the approval of mifepristone, the first pill in a two-drug regimen.

The plaintiffs claim that mifepristone is unsafe and that the F.D.A. did not follow proper regulatory protocols in approving it in 2000 — contentions that the government strongly disputes, citing years of research and other support for the agency’s actions.

The panel, composed of two appointees by President Donald J. Trump, Judges James C. Ho and Cory T. Wilson, and a George W. Bush appointee, Judge Jennifer Walker Elrod, did not issue a decision at the hearing on Wednesday. That will come later, although there is no deadline for the court to decide. Any decision is likely to be appealed, first to the full appellate court and then to the Supreme Court.

In a preliminary ruling in April, Judge Matthew J. Kacsmaryk of the Northern District of Texas, a Trump appointee who is a longtime opponent of abortion, suspended the F.D.A.’s approval of the drug.

Central to the arguments on Wednesday will be whether the plaintiffs — four anti-abortion doctors and an umbrella group called the Alliance for Hippocratic Medicine — could show they would suffer actual injuries if access and approval of the pill remains unchanged. Lawyers call this requirement standing.

In a brief filed to the Fifth Circuit, the plaintiffs said that the F.D.A.’s continuing approval of mifepristone would force emergency room doctors who oppose abortion to treat patients who experience complications after taking mifepristone. The brief said that the situation would subject doctors to “enormous stress and pressure” and put them at odds with their religious beliefs.

The F.D.A. has vigorously disputed that the plaintiffs have suffered, or would suffer, real injury from the continued availability of the pill.

The plaintiffs “neither take nor prescribe mifepristone,” lawyers for the F.D.A. wrote in their brief. And because many studies have shown that complications from medication abortion are rare, with less than 1 percent of patients needing hospitalization, there is little chance that anti-abortion doctors would encounter any patients needing treatment after taking abortion pills, the government has argued.

A lower-court order invalidating approval of the drug “would upend the status quo based on the court’s deeply misguided assessment of mifepristone’s safety,” the F.D.A.’s brief added. Mifepristone is also used to help patients who are experiencing miscarriages, so any decision in this case could affect miscarriage treatment as well.

Also in dispute is whether the plaintiffs can even challenge the approval process for a drug that has been on the market for 23 years.

The plaintiffs’ brief claimed that the F.D.A. unlawfully approved mifepristone in a flawed process that “put politics above women’s health” and then made “politically driven decisions to unlawfully push a dangerous regimen.”

The government strongly pushed back in its brief, saying, “F.D.A.’s actions were amply supported by a record developed over decades of safe and effective use of mifepristone in the United States and around the world.”

The agency also argued that the plaintiffs waited too long to bring their case.

“They did not sue until more than two decades after mifepristone’s approval,” the lawyers for the F.D.A. wrote.

More than a dozen medical associations filed friend-of-the-court briefs in support of the agency.

In one brief, medical associations questioned the reasoning behind a ruling by the federal judge in Texas, saying it relied on “pseudoscience and on speculation.”

Judge Kacsmaryk, they wrote, ignored “decades of unambiguous analysis supporting the use of mifepristone in miscarriage and abortion care.”