WASHINGTON The Senate Judiciary Committee has asked Texas billionaire Harlan Crow to detail gifts he or his companies have made to U.S. Supreme Court Justice Clarence Thomas, the panel said on Tuesday.

"Recent investigative reporting has identified multiple instances in which you or entities you own or control have made payments, purchased real estate, or provided gifts, travel, or other items of value to Supreme Court Justice Clarence Thomas and members of his family," read the letter from committee Democrats including its chairman, Senator Dick Durbin.

"Many of these gifts, transactions, and items of value had not been previously disclosed by Justice Thomas," it said.

Similar letters, dated Monday, were sent to the holding companies that own Crow's private jet and private yacht.

The Democratic-led Senate panel last week explored the possibility of pursuing legislation to impose ethics standards on the Supreme Court amid revelations about luxury trips and real estate transactions by conservative justices, but the panel's Republican members voiced stern opposition.

The news outlet ProPublica has detailed ties between Thomas, a conservative who is the court's longest-tenured member, and wealthy Republican donor Crow, including real estate purchases and luxury travel paid for by the Dallas businessman.

The letter said Crow has acknowledged items of value given to Thomas and his family in public statements.

It asked him to provide the information to the committee by May 22 as the panel works to craft legislation strengthening ethics rules and standards for Supreme Court justices.

(Reporting by Doina Chiacu; Editing by Mark Porter)