Supreme Court Chief Justice John Roberts on Tuesday declined an invite to testify before the Senate Judiciary Committee on court ethics in the wake of reports of Justice Clarence Thomas’ close friendship with a Republican megadonor.

In a letter declining Senate Judiciary Committee Chairman Dick Durbin’s (D-Ill) invitation, Roberts noted that chief justices of the high court have only testified before the Senate twice in the past 102 years. 

“I must respectfully decline your invitation,” Roberts wrote in the missive. 

“Testimony before the Senate Judiciary Committee by the Chief Justice of the United States is exceedingly rare as one might expect in light of separation of powers concerns and the importance of preserving judicial independence,” he added.

Roberts also pointed out that testimony to Congress by the president of the United States is similarly infrequent. 

“No President has ever testified before the Senate Judiciary Committee, and only three Presidents (in 1862, 1919, and 1974) have testified before any Congressional committee,” Roberts wrote. 

Along with his letter, the chief justice passed along the court’s Statement of Ethics Principles and Practices “to which all of the current Members of the Supreme Court subscribe.” 

Durbin said in a statement on Tuesday that the Senate will take on Supreme Court ethics reform “whether the Court participates in the process or not.”

“I am surprised that the Chief Justice’s recounting of existing legal standards of ethics suggests current law is adequate and ignores the obvious. The actions of one Justice, including trips on yachts and private jets, were not reported to the public. That same Justice failed to disclose the sale of properties he partly owned to a party with interests before the Supreme Court,” Durbin said Tuesday.

“It is time for Congress to accept its responsibility to establish an enforceable code of ethics for the Supreme Court, the only agency of our government without it,” added Durbin.

Earlier this month, Supreme Court Justice Clarence Thomas confirmed reports by ProPublica that he had repeatedly accepted travel from wealthy Republican donor Harlan Crow over their more than two decades of friendship.

Thomas contends that he did not have to report the gifts on annual financial disclosure forms.