WASHINGTON (BLOOMBERG, AFP) - US President Joe Biden urged the election of more lawmakers who support abortion rights and said he’d seek to enshrine the protections of Roe v Wade into US law, following a report that the Supreme Court is poised to overturn the landmark ruling.

“At the federal level, we will need more pro-choice senators and a pro-choice majority in the House to adopt legislation that codifies Roe, which I will work to pass and sign into law,” Biden said in a statement on Tuesday (May 3).

The United States Supreme Court is poised to overturn the landmark Roe versus Wade decision protecting the constitutional right to abortion, according to a draft majority opinion circulated inside the court, Politico reported on Monday.

The draft opinion, which Politico said it got from a person familiar with the court's deliberations, was written by Justice Samuel Alito and has at least preliminary support from four other Republican-appointed justices, the publication said.

“We do not know whether this draft is genuine, or whether it reflects the final decision of the Court,” Biden said.

The court is scheduled to rule by July in the case.

"Roe was egregiously wrong from the start," Justice Alito wrote, according to Politico.

"It is time to heed the Constitution and return the issue of abortion to the people's elected representatives."

Supreme Court Chief Justice John Roberts said on Tuesday that the draft opinion on abortion leaked to the press was authentic, but not the final decision on the matter.

Roberts also said in a statement that he had directed the marshal of the court to launch an investigation into the source of the extraordinary leak.

A ruling overturning Roe would be transformational - legally, politically and socially.

Twenty-six states would be likely to ban most abortions, according to the Guttmacher Institute, a research organisation that backs abortion rights. That shift would come even as countries elsewhere liberalise their abortion laws.

News of the draft ruling comes one day ahead of primary voting in Ohio and Indiana.

Overturning Roe could serve to roil midterm elections in November that were set to be a referendum on inflation, crime, immigration and Covid-19.

Disclosure of the draft opinion also marks an extraordinary breach of protocol for an institution that has long prided itself for being almost leak-proof.

In the Supreme Court's modern history, no draft decision has been disclosed publicly while a case was pending.

Supreme Court spokesman Patricia McCabe said the court had no comment.

Politico said Justices Clarence Thomas, Neil Gorsuch, Brett Kavanaugh and Amy Coney Barrett voted with Alito in the private conference the court held after arguments in December.

The publication said Chief Justice John Roberts' ultimate vote was unclear and the court's three Democratic appointees were planning to dissent.

A ruling overturning Roe "would deprive half the nation of a fundamental, constitutional right that has been enjoyed by millions of women for over 50 years", American Civil Liberties Union Executive Director Anthony Romero said in a statement.

"The breach in protocol at the court pales in comparison to the breach in constitutional freedoms that the court is charged with upholding."

Mr Neal Katyal, who served as President Barack Obama's top Supreme Court lawyer, tweeted that the draft decision looks legitimate and likened it to the Pentagon Papers - a massive document leak that helped turn the American public against the war in Vietnam.

A majority of the US public has consistently supported keeping abortion legal in all or at least some cases since the mid-1970s, according to Gallup data, while only about one in five Americans say the procedure should be illegal under all circumstances.

Other polls show similar trends.

A Marquette University poll earlier this year found that 72 per cent of Americans oppose overturning the Roe v. Wade ruling.

"An extremist Supreme Court is poised to overturn #RoeVWade and impose its far-right unpopular views on the entire country," Democratic Senator Elizabeth Warren of Massachusetts tweeted.

Congress’ top two Democrats – Senate Majority Leader Chuck Schumer and House Speaker Nancy Pelosi – said in a statement Monday night that the decision “would go down as an abomination, one of the worst and most damaging decisions in modern history”. 

Republican Senator Josh Hawley of Missouri, a former law clerk to Roberts on the court, tweeted that the leak was an "assault" by the left that was "clearly meant to intimidate" the court.

Ms Lynn Fitch, the Republican Mississippi attorney general whose appeal called on the court to overturn Roe, tweeted that the veracity of the linked opinion can't be verified.

She said the state would "let the Supreme Court speak for itself and wait for the court's official opinion".

The opinion was labelled "1st draft" and included a stamp indicating it was circulated to the other justices on Feb 10.

Supreme Court justices occasionally switch sides in cases after the initial vote.

The justices are considering a Mississippi law that would ban abortion after 15 weeks of pregnancy.

During arguments on Dec 1, Justice Roberts suggested interest in upholding the Mississippi law without explicitly overturning Roe and the 1992 Planned Parenthood versus Casey ruling.

Casey said states can't impose significant obstacles on abortion before fetal viability, which the court suggested was around 23 or 24 weeks at the time.

A move by the US to limit abortion rights would mark one of the few global instances of a nation reversing course.

In the past few years, several nations - notably in Latin America - have eased restrictions on abortions.