A lawsuit that could test the constitutionality of the nation’s most restrictive abortion ban was filed in Texas on Monday against a doctor who admitted to performing an abortion considered illegal under the new law.

The details of the civil suit against Alan Braid, a physician in San Antonio, are as unusual as the law itself, which empowers private citizens to enforce the ban on abortion once cardiac activity has been detected — often as early as six weeks into a pregnancy.

The plaintiff is a felon serving a federal sentence at home in Arkansas, with no connection to the abortion at issue. He said he filed the claim not because of strongly held views about reproductive rights but in part because of the $10,000 he could receive if the lawsuit is successful. A second suit filed Monday — just four paragraphs long — came from a man in Chicago who asked a state court to strike down the abortion law as invalid.

Since the Texas ban took effect Sept. 1, advocates on both sides of the abortion debate have been anticipating such lawsuits, though perhaps not from a “disbarred and disgraced former Arkansas lawyer,” as Oscar Stilley described himself in his complaint.

The Supreme Court’s conservative majority said this month that an initial challenge to the law raised serious constitutional questions. But the majority allowed the law to stand and indicated that because abortion providers had sued state officials — and not private citizens charged with enforcing the ban — the court could not immediately weigh in.

The nation remains sharply divided over abortion rights, with a growing number of Republican-led state legislatures trying to limit or ban the procedure. Also Monday, the Supreme Court scheduled arguments for Dec. 1 in a Mississippi case that tests Roe v. Wade, the 1973 Supreme Court decision guaranteeing the right to an abortion before viability, which is usually 22 to 24 weeks into a pregnancy.

In Texas, Braid stepped forward last week to say that he had performed an abortion for a woman who was in the early stages of a pregnancy but beyond the state’s new limit. Despite the legal risks, Braid said in a Washington Post op-ed that he acted because of his duty as a doctor and “because she has a fundamental right to receive this care.”

Stilley, the Arkansas man, said he decided to sue after reading a news report about Braid’s declaration. A former lawyer convicted of tax fraud in 2010 and sentenced to 15 years, Stilley said in an interview that he is not personally opposed to abortion but thinks the measure should be subject to judicial review.

“If the law is no good, why should we have to go through a long, drawn-out process to find out if it’s garbage?” he said after filing the complaint in state court in Bexar County, which includes San Antonio. Stilley also noted that a successful lawsuit could result in a “bounty” of at least $10,000 for the plaintiff.

Braid, whose clinics are represented by the Center for Reproductive Rights, declined to comment through the legal organization.

“S.B. 8 says that ‘any person’ can sue over a violation, and we are starting to see that happen, including by out-of-state claimants,” Marc Hearron, the group’s senior counsel, said in a statement.

Texas Right to Life, an antiabortion group, quickly disavowed the lawsuits as “self-serving legal stunts.”

“We believe Braid published his op-ed intending to attract imprudent lawsuits, but none came from the Pro-Life movement,” John Seago, the organization’s legislative director, said in a statement. “Texas Right to Life is resolute in ensuring the Texas Heartbeat Act is fully enforced.”

The Texas law was deliberately designed to avoid judicial scrutiny by barring state officials, who would typically be the target of lawsuits, from enforcing the ban.

Abortion providers sued to try to stop the Texas law. But the high court allowed the measure to stand while litigation continues.

In a 5-to-4 order, the court’s conservative majority said opponents who sued state judges and court clerks had not clearly shown that their lawsuit targeted the right people because government officials cannot enforce the law.

The Biden administration separately sued Texas this month to block the law. A judge in Austin has set a hearing in that case for Oct. 1.

After publication of Braid’s column, conservative legal commentator Ed Whelan discouraged supporters of the law from suing the doctor and giving him the “test case that he is seeking.”

Whelan wrote Monday that private citizens should not bring a civil enforcement action until the Supreme Court has ruled in the Mississippi case, which asks the justices to overrule Roe.

Melissa Murray, a professor at New York University School of Law, said lawsuits like the one Stilley filed on Monday were “never the principal goal” of the Texas law. The main point, she said, was to avoid a preemptive legal challenge and to “absolutely bring reproductive care in Texas to a standstill. That was always the endgame.”

Until Braid’s public admission, abortion clinics in Texas said they were abiding by the new restrictions and sending people to Oklahoma, Kansas and New Mexico to terminate pregnancies.

The law bars abortion at a time when many women do not yet realize they are pregnant. There are no exceptions in the law for rape, sexual abuse or incest.

Braid, who owns Alamo Women’s Reproductive Services, has met with patients seeking abortions every day since the ban took effect. More people have been making appointments earlier in their pregnancies, Braid told The Post in an interview before the publication of his op-ed.

“There’s an awful feeling in the room until we can confirm their gestational age,” he said. Some patients start sobbing when he tells them they are too far along to terminate their pregnancies under the new Texas law, he said. Others cry when he says they’re under the limit, relieved that they can proceed.

Operation Rescue, an antiabortion group, filed a complaint against Braid on Monday asking state officials to revoke the doctor’s medical license. In a letter to the Texas Medical Board, the group’s senior vice president requested an investigation into Braid’s “illegal conduct” outlined in the op-ed, and an emergency suspension of his license “to prevent him from further violating Texas law.”

Cheryl Sullenger wrote that because of Braid’s “defiant attitude and his unlawful act, he has committed unprofessional conduct.”

Braid said in his op-ed that he has discussed with patients how they might access abortion services in another state. He advised one woman, who is 42 with four children, to travel to Oklahoma — a nine-hour drive one way — and offered to help with funding.

“She told me she couldn’t go even if we flew her in a private jet,” he wrote. “ ‘Who’s going to take care of my kids?’ she asked me. ‘What about my job? I can’t miss work.’ ”