The Supreme Court on Monday heard arguments to Texas' controversial abortion law, which has virtually ended abortion after six weeks of pregnancy in the nation’s second-largest state and made waves nationwide.

The Texas law, known as S.B. 8, was signed into law by Gov. Greg Abbott in May. The restrictive law prohibits abortion after cardiac activity is detected in a fetus, usually around six weeks – before some women know they are pregnant. The law makes exceptions for medical emergencies, but not rape or incest.

The justices heard arguments Monday in two cases over whether abortion providers or the Justice Department can mount federal court challenges to the law, which has an unusual enforcement scheme its defenders argue shield it from federal court review.

Justices Amy Coney Barrett and Brett Kavanaugh, who were both appointed by former President Donald Trump and voted earlier this year to allow the law to go into effect, raised serious questions about the law's structure, seeming to indicate they may allow abortion providers to challenge it.

Justice Kavanaugh, who previously allowed the law to take effect in September in a decision that split the court 5-4, suggested that the unusual enforcement scheme – which allows citizens to sue over abortions instead of state officials enforcing the law – could be problematic.

“There’s a loophole that’s been exploited here, or used here,” he said, explaining that the question for the court is whether to “close that loophole.” Kavanaugh suggested that the “principle” and “whole sweep” of a 1908 Supreme Court case would “suggest extending the principle here, arguably” and closing the loophole.

 The law, written to make it difficult to mount legal challenges, subjects clinics, doctors and any others who facilitate abortions to large financial penalties.

“Millions and millions retroactively imposed, even though the activity was perfectly lawful under all court orders and precedent at the time it was undertaken, right?” Kavanaugh asked, one of several skeptical questions he put to Texas solicitor general Judd Stone.

In neither case is the right to an abortion directly at issue, but the motivation for lawsuits filed by abortion providers and the Justice Department is that the Texas law conflicts with landmark Supreme Court rulings that prevent a state from banning abortion early in pregnancy. The question on the table in the DOJ lawsuit is whether or not the federal government has the ability to sue Texas to block the law.

“Each state has a responsibility to do what they think is right, and their legislators have have a responsibility to represent their constituents' views," said Attorney General Ken Paxton outside the Supreme Court on Monday.

The founder of Whole Woman's Health, one abortion provider that sued over the law, said the impact of the law has been devastating.

"It's been awful. I mean, we've had to deny care to probably about 80% of the people that come to the clinic," said Amy Hagstrom Miller. "This law is designed to make people afraid and confused and to be unsure of what their rights are. Many people who come to us are parenting already, and can't just sort of pick up and get time off work and childcare in order to travel to one of our surrounding states."

Newly minted Solicitor General Elizabeth Prelogar, arguing her first case on behalf of the United States since being confirmed to the role by the Senate last week, called the law "an attack on the authority of this court to say what the law is." Prelogar arugued that the restrictive law was enacted in "open defiance" of Supreme Court precedent.

When asked by Justice Clarence Thomas what the federal government's formal interest is in suing Texas over S.B. 8, Prelogar replied that the U.S. has an interest in protecting federal law when a state flouts its supremacy.

"The United States may sue to protect the supremacy of federal law against this attack," Prelogar argued.

When Thomas followed up to ask if there are any examples of the U.S. intervening in such a way to protect a constitutional right, Prelogar argued that the Texas law has no precedent.

Prior to Prelogar's arguments, the court first heard from Marc Hearron, senior counsel for the Center for Reproductive Rights who is arguing on behalf of the abortion providers.

Hearron took a similar tact to the argument Prelogar later presented: "At issue here is nothing less than the supremacy of federal law," he said.

In a notable exchange, Justice Barrett, the newest member to the high court, asked Hearron if the Texas law, as written, limits a defendant's ability to mount a constitutional defense in state court: "The full constitutional defense cannot be asserted in the defensive posture, am I right?" Hearron replied that was their understanding of the law.

Barrett also pressed Stone about provisions of the law that force providers to fight lawsuits one by one and, she said, don’t allow their constitutional rights to be “fully aired.”

Hearron argued in his closing remarks that S.B. 8 "will provide a roadmap for other states to abrogate other rights that have been recognized by this court."

Justice Elena Kagan told Stone that until Texas passed its law, “no state dreamed” of trying to make an end-run around Supreme Court precedent in the same way.

If the Supreme Court doesn’t do anything about that, she said, it would be inviting states to try to flout precedent: “Guns. Same-sex marriage. Religious rights. Whatever you don’t like: go ahead,” she said. Kagan, who disagreed with her colleagues’ decision to let the law take effect, said Texas’ law has prevented women in Texas “from exercising a constitutional right.”

The justices will hear a separate challenge to the decisions in Roe v. Wade and Planned Parenthood v. Casey in a case over Mississippi’s ban on abortion after 15 weeks. Those arguments are set for Dec. 1.

The Texas law has been in effect since September, except for a 48-hour period in early October when it was blocked by a lower court.

The high court jumped into the Texas cases less than two weeks ago, moving at extraordinary speed, but only after rejecting a plea to block the law by a 5-4 vote in early September. The high court did not rule on the constitutionality of the law in its decision.

Five conservative justices, including three who were appointed by President Donald Trump, were in the majority. Chief Justice John Roberts joined the court’s three liberal justices in dissent.

At least 12 other states have enacted bans early in pregnancy, but all have been blocked from going into effect.

But rather than have state officials enforce it, the Texas law deputizes private citizens to sue anyone who performs or aids and abets an abortion. If they’re successful, they are entitled to at least $10,000. Women who obtain abortions can’t be sued under the law.

The structure of the law threatens abortion providers with huge financial penalties if they violate it. Clinics throughout the state have stopped performing abortions once cardiac activity is found.

The result, both the providers and the Biden administration said, is that women who are financially able have traveled to other states and those without the means must either continue their pregnancies against their will or find other, potentially dangerous ways to end them.

“We’ve had two life-saving months in the state of Texas, where it’s the first time in 50 years abortion has been really regulated in the state," said Chelsea Youman, National Legislative Advisor at Human Coalition Action, a pro-life organization.

The state and Jonathan Mitchell, an architect of the law, say in their briefs that the providers and the Justice Department lack the right to go into federal court and can’t sue state judges and clerks who are not responsible for enforcing the abortion ban. They also contend that there is no effective way of blocking the law, in part because federal court can’t force state judges to abstain from hearing the lawsuits the law authorizes.

The Associated Press contributed to this report.