(Bloomberg) -- All Democrats on the Senate Judiciary Committee have called on Chief Justice John Roberts to investigate undisclosed luxury trips that Supreme Court Justice Clarence Thomas accepted from a wealthy Republican donor. 

The panel, the Democrats said in a Monday letter, would soon hold a hearing on the court’s ethical standards.

The committee “has a role to play in ensuring that the nation’s highest court does not have the federal judiciary’s lowest ethical standards,” the senators, led by Chairman Dick Durbin, said in the letter.

“You have a role to play as well, both in investigating how such conduct could take place at the court under your watch, and in ensuring that such conduct does not happen again.”

The lawmakers also asked Roberts to take the lead in adopting a code of conduct that would for the first time subject the justices to the types of standards now applied to lower courts, and vowed to consider legislation to resolve the issue if the Supreme Court does not act on its own.

A ProPublica report last week detailed gifts of trips on jets and private yachts, as well as luxury accommodations, accepted by Thomas over two decades from Dallas real estate magnate Harlan Crow but never reported. That included a 2019 “island hopping” vacation with costs that “could have exceeded $500,000,” along with travel to California’s Bohemian Grove retreat for men, and Crow’s East Texas ranch.

Thomas last Friday issued a one-paragraph statement defending himself, saying he’d sought guidance from colleagues and others in the judiciary early in his 32-year tenure on the Supreme Court. He said he was “advised that this sort of personal hospitality from close personal friends, who did not have business before the court, was not reportable.”

It did little to assuage the 74-year-old justice’s critics, who insist the lack of reporting ran afoul of a Watergate-era law requiring justices and other federal officials to disclose most gifts they receive and that tougher rules for the justices are needed. The nine justices of the Supreme Court are the only federal judges who aren’t formally bound by a code of conduct.

Roberts in the past has not embraced the idea of the court taking action. In a 2011 year-end Supreme Court report, he said “the court has had no reason to adopt the Code of Conduct as its definitive source of ethical guidance.”

Even as Senate Democrats are suggesting legislation could come, its prospects would be in doubt. Republicans have been silent in recent days about the matter, and at least nine Senate Republicans would have to back legislation for it to proceed to the floor in that chamber. Republicans control the House.

--With assistance from Greg Stohr.

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