Billionaire Harlan Crow has refused to comply with a request by Senate Finance Chair Ron Wyden for a complete accounting of Crow’s gifts to Supreme Court Justice Clarence Thomas.

According to Ryan Carey, a spokesperson for Wyden (D-Ore.), the Senate tax chief received an “obstructive letter” from a lawyer for Crow late Monday night declining to answer a series of questions about the billionaire’s financial arrangements with Thomas that Wyden posed to Crow in an April 24 letter.

The Finance Committee is expected to respond shortly. Wyden has previously said he would “explore using other tools at the committee’s disposal” should Crow not cooperate with the request.

Wyden’s next steps could include subpoenaing Crow for the requested records or using a section of the tax code that vests the chairs of Congress’ tax committees with the authority to obtain a private citizen’s tax returns directly from Treasury — a power that House Democrats used last year to publish the taxes of former President Donald Trump.

Meanwhile, Sen. Mike Crapo, the top Republican on the Finance Committee, made it clear Tuesday that he would oppose any such efforts, saying they would “undermine the independence of the Supreme Court and its individual Justices.”

Sen. Mike Lee (R-Utah) and 13 other Republican senators also wrote to Wyden on Monday to express concerns about Wyden’s request to Crow. The GOP lawmakers asserted the demands amounted to intimidation of a private citizen that had the ultimate goal of discrediting Thomas.

“We reject this manufactured ‘ethics crisis’ at the Supreme Court as a ploy to further Democrats’ efforts to undermine public confidence and change the makeup of the Court,” the Republicans wrote.

In his letter, Wyden asked for details on the gifts Crow lavished on Thomas for over two decades, as reported by ProPublica, that included trips aboard the billionaire’s superyacht to Indonesia, New Zealand and Greece and free use of his private jet.

Although Thomas neglected to report the gifts on his annual disclosure forms, Wyden argued they were substantial enough that Crow would have been obligated to report them on his annual gift tax returns to the IRS.