The United States is in political uproar over a leaked document from its Supreme Court, which indicates abortion rights are about to be rolled back across much of the country.

Overnight the court's Chief Justice, John Roberts, confirmed a draft opinion published by the news website Politico yesterday was "authentic".

He described the leak as a "betrayal of the confidences of the court" and "an egregious breach of trust", and said there would be an investigation.

The draft, written by conservative Justice Samuel Alito, would overrule the landmark 1973 Supreme Court decision in Roe vs Wade, which has underpinned abortion rights in the US for the past 50 years.

Under the precedent set by Roe, and a subsequent decision in the 1992 case Planned Parenthood vs Casey, governments across the US can only ban abortion from the point of "viability" onwards, meaning the time at which a foetus can realistically survive outside the womb. That threshold is reached at about 23 or 24 weeks of pregnancy.

Overturning those rulings would allow state governments to ban abortion far earlier. Some states already have laws on the books – currently unenforceable – that will trigger bans from 15 weeks, or even as early as six weeks, when many women don't know they're pregnant.

"Roe was egregiously wrong from the start," Justice Alito writes in the draft opinion.

"Its reasoning was exceptionally weak, and the decision has had damaging consequences. Far from bringing about a national settlement of the abortion issue, Roe and Casey have inflamed debate and deepened division.

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

"We hold that Roe and Casey must be overruled.

- Sam Clench and Brooke Rolfe, news.com.au