A majority on the US Supreme Court appeared to be leaning Monday towards blocking a Texas bill that bans abortion after six weeks, the most restrictive law passed since abortion was made a constitutional right five decades ago.

A previous bid by abortion providers to halt enforcement of the "Texas Heartbeat Act" had failed in the nation's highest court two months ago by a 5-4 margin.

Police officers stand by security barricades set up outside the US Supreme Court ahead of legal challenges to a restrictive abortion law passed by Texas
Police officers stand by security barricades set up outside the US Supreme Court ahead of legal challenges to a restrictive abortion law passed by Texas GETTY IMAGES / Drew Angerer

But two conservative justices appointed by former president Donald Trump -- Brett Kavanaugh and Amy Coney Barrett -- appeared inclined after two hours of oral arguments to join Chief Justice John Roberts and the three liberal justices in challenging the Texas law.

Laws restricting abortion have been passed in multiple Republican-led states but struck down by the courts because they violated previous Supreme Court rulings that guaranteed the right to an abortion until the fetus is viable outside the womb, typically around 22 to 24 weeks.

Texas Senate Bill 8 (SB8) differs from other efforts in that it attempts to insulate the state by giving members of the public the right to sue doctors who perform abortions -- or anyone who helps facilitate them -- once a heartbeat in the womb is detected.

Anti-abortion demonstrators outside the US Supreme Court
Anti-abortion demonstrators outside the US Supreme Court GETTY IMAGES / Drew Angerer

They can be rewarded with $10,000 for initiating civil suits that land in court, prompting criticism that the state is encouraging people to take the law into their own hands.

Kavanaugh, in particular, appeared skeptical about the mechanics of the Texas law, asking the state Solicitor General Judd Stone about the "implications for other constitutional rights."

He said Texas seemed to be trying to take advantage of a "loophole" and asked why other states could not pass similar laws to target free speech rights, or gun laws or the free exercise of religion.

A protestor for women's abortion rights outside the US Supreme Court
A protestor for women's abortion rights outside the US Supreme Court AFP / MANDEL NGAN

For example, Kavanaugh asked, what if "anyone who sells an AR-15 is liable for a million dollars to any citizen?"

Stone argued that it was up to Congress to decide what rights to protect, but in the abortion case, it is not the state of Texas that is enforcing the law but private individuals.

The nine justices of the US Supreme Court
The nine justices of the US Supreme Court POOL / Erin Schaff

Marc Hearron of the Center for Reproductive Rights, who argued before the court on behalf of abortion providers, said he was "happy to see that several of the justices had serious concerns."

"We do hope for relief from the Supreme Court as soon as possible," Hearron said. "We obviously hope for a very quick ruling."

Protesters gather outside the US Supreme Court during a hearing on the Texas anti-abortion law
Protesters gather outside the US Supreme Court during a hearing on the Texas anti-abortion law AFPTV / Bastien INZAURRALDE

Julia Kaye, an attorney with the American Civil Liberties Union, was also optimistic.

"It is certainly promising that there were more than four justices asking questions today that seem to recognize that SB8 is an affront to the Constitution and could be a blueprint for states looking to target other federal rights that they disfavor," Kaye said.

Dozens of protesters gathered outside the court in Washington as the Supreme Court heard legal challenges to the Texas law, which makes no exceptions for rape or incest.

"Keep Your Laws Off Our Bodies," read signs carried by demonstrators supporting the right to an abortion.

Anti-abortion protesters were there, too, holding placards that read, "Let Their Hearts Beat."

The Texas law bans abortions after a heartbeat can be detected in the womb, which is normally around six weeks -- before many women even know they are pregnant.

Abortion providers have asked the Supreme Court to block state clerks in Texas from accepting suits under SB8, and the court -- after declining to do so previously, citing "procedural issues" -- appeared inclined to do so this time around.

Democratic President Joe Biden's Justice Department has also sued Texas, arguing that the restrictions on abortion imposed by the second-largest US state are unconstitutional.

"The most pernicious thing about the Texas law is it sort of creates a vigilante system, where people get rewards," Biden said in September.

Many clinics in Texas -- fearful of potentially ruinous lawsuits -- have closed their doors, and the number of abortions in the state fell to 2,100 in September from 4,300 a year earlier, according to a University of Texas study.

The Supreme Court could make a decision at any time after oral arguments but is widely expected to rule before hearing another abortion case on December 1 that takes direct aim at Roe v. Wade.

In that case, the court will hear a challenge to a Mississippi law that bans abortion after 15 weeks.