US Supreme Court nominee Brett Kavanaugh once questioned whether the landmark decision affirming women's right to abortion access was the “settled law of the land,” according to leaked emails.

Mr Kavanaugh, Donald Trump’s pick to replace retiring Justice Anthony Kennedy on the Supreme Court, questioned the underpinnings of the case – Roe v Wade – as a lawyer for former President George W Bush’s White House.

His comments came in an email suggesting changes to an op-ed article that read, in part: “It is widely accepted by legal scholars across the board that Roe v Wade and its progeny are the settled law of the land”.

“I am not sure that all legal scholars refer to Roe as the settled law of the land at the Supreme Court level since Court can always overrule its precedent, and three current Justices on the Court would do so,” Mr Kavanaugh wrote in response, according to emails obtained by the New York Times.

Mr Kavanaugh's opinion on Roe v Wade has been one of the defining issues of his confirmation hearing, as women’s rights advocates fear the conservative judge could tip the balance of the court against the landmark 1973 ruling.

Supreme Court nominee Brett Kavanaugh delivers opening statement

Mr Kavanaugh has so far refused to say whether he would support overturning the decision, saying only that it is an “important precedent” that has been reaffirmed many times.

The judge was similarly evasive when Democratic Senator Dianne Feinstein questioned him about the emails during his hearing on Thursday, saying he was only referring to the views of other legal scholars.

"I think [the op-ed] was overstating something about legal scholars, and I’m always concerned about accuracy," Mr Kavanaugh said.

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The email was met with outcry from women’s rights organisations – many of which have been organising against the nominee for months, out of fear that he would threaten reproductive rights.

"Donald Trump promised to nominate anti-choice justices. These documents show that he fulfilled that promise. Brett Kavanaugh is a clear threat to Roe v Wade,” said Stephanie Schriock, president of women’s political organisation EMILY's List, in a statement.

Others were more concerned that the email, and hundreds like it, were being kept from the general public. A lawyer for the Bush administration turned over thousands of Mr Kavanaugh’s emails on Monday, but deemed them “committee confidential,” meaning they could not be published or even discussed during the confirmation hearing.