Chief Justice John Roberts on Tuesday declined an invitation from a senior Democratic senator to testify at a congressional hearing on ethics rules for members of the Supreme Court.

In a letter to Senate Judiciary Committee Chairman Dick Durbin, Roberts suggested that his participation in the hearing could pose a threat to judicial independence.

“Testimony before the Senate Judiciary Committee by the Chief Justice of the United States is extremely rare, as might be expected in light of concerns about the separation of powers and the importance of preserving judicial independence,” Roberts wrote. .

Roberts included in his letter a statement of ethical principles and practices «to which all current members of the Supreme Court subscribe.»

Durbin, D-Illinois, had requested the participation of Robertsor the participation of a judge of their choice, in a public hearing «on the ethical norms that govern the Justices of the Supreme Court and the possible reforms to said norms», scheduled for May 2.

In his invitation, Durbin cited «ample precedent» for testimony from sitting judges, citing October 2011 testimony from then-Justices Stephen Breyer and Antonin Scalia, which he said included «robust exchanges on the approach to the court in matters of ethics.

The tug-of-war comes after a ProPublica report this month described how billionaire Republican megadonor Harlan Crow provided trips and gifts to Clarence Thomas that were not disclosed by conservative justice.

After Roberts refused to testify, Durbin referenced Thomas, saying lawmakers should establish «an enforceable code of ethics» for the Supreme Court.

“I am surprised that the Chief Justice’s account of existing legal ethical standards suggests that the current law is adequate and ignores the obvious. A judge’s actions, including trips on yachts and private planes, were not reported to the public. That same judge failed to disclose the sale of properties he owned in part to an interest party before the Supreme Court,” Durbin said.

«It is time for Congress to accept its responsibility to establish an applicable code of ethics for the Supreme Court, the only agency of our government without it,» he added.

In addition to seeking his testimony, Democrats on the Senate Judiciary Committee have called on Roberts to investigate Thomas’ undisclosed gifts.

Thomas issued a statement this month calling Crow and his wife, Kathy, «dearest friends» and saying he had been told early in his Supreme Court tenure that «the personal hospitality of close personal friends, that they had no business before the Cut, it was not reportable.”

“I have endeavored to follow that advice during my tenure and have always tried to adhere to disclosure guidelines,” Thomas said in the statement.

On Monday, Senate Finance Committee Chairman Ron Wyden launched a separate investigation into the matter, asking Crow to provide a full accounting of any travel, gifts, and Payments has done to Thomas over the years.

The allegations against Thomas were referred last week to the Judicial Conference of the United States, a committee that reviews financial disclosures, in response to concerns raised by Sen. Sheldon Whitehouse, DR.I., and Rep. Hank Johnson, D. -Ga.

frank thorp and Lawrence Hurley contributed.