Supreme Court Justice Clarence Thomas has been accused by a top Democratic senator of failing to disclose two flights on a private jet owned by a billionaire Republican donor.

Ron Wyden, chairman of the Senate Finance Committee, said that Justice Thomas did not declare a roundtrip from Hawaii to New Zealand with his wife on Harlan Crow’s private jet in 2010.

He used a letter to Mr Crow’s lawyer to accuse the property mogul of “showering a public official with extravagant gifts then writing off those gifts to lower his tax”.

A spokesman for Mr Crow told US media Mr Wyden’s inquiries had “no legal basis and are only intended to harass a private citizen”, and that Mr Crow had “always followed applicable tax law”.

“It’s concerning that Senator Wyden is abusing his committee’s powers as part of a politically motivated campaign against the Supreme Court,” said a spokesman for Mr Crow, Michael Zona.

Justice Thomas has not commented publicly on the letter. The Supreme Court did not immediately respond to an inquiry from the BBC.

Justice Thomas has previously said that he believed he did not need to report trips with close friends who do not have business before the Supreme Court.

It is the latest criticism against the conservative judge, whose previous travel on private jets and yachts have previously come under scrutiny.

Under a new disclosure system, the judge in June amended his annual statement to include two trips with Mr Crow in 2019 – one to Bali and another to California.

However, Mr Wyden alleged in his letter that the judge had used private jets paid for by Mr Crow at least 17 times in the last eight years.

The Oregon senator also cited a new trip that he said had not been reported publicly.

Mr Wyden cited US Customs and Border Protection records of a trip from Hawaii to New Zealand in 2010 by the judge and his wife, Virginia, on Mr Crow’s private jet.

The White House said Mr Wyden’s letter strengthened President Joe Biden’s case for sweeping reforms to the court, which is currently dominated by conservatives.

Mr Biden last week proposed establishing term limits for justices, which are currently lifetime appointments, and an enforceable code of conduct.

Such changes would be difficult to pass in Congress.

The White House said on Monday that “the most powerful court in the United States shouldn’t be subject to the lowest ethical standards, and conflicts of interest on the Supreme Court cannot go unchecked”.

The heightened focus on court ethics has drawn scrutiny to other Supreme Court members.

It emerged last year that Justice Sonia Sotomayor, a liberal, did not recuse herself from three cases involving Penguin Random House, which had paid her more than $3m (£2.4m).