Updated April 25, 2023 at 8:39 PM ET

Chief Justice John Roberts has declined an invitation from Sen. Dick Durbin, D-Ill., chair of the Senate Judiciary Committee, to testify before the panel, calling such testimony by chief justices "exceedingly rare."

The Senate panel had planned to hold a hearing on May 2 to examine what Durbin called "common sense proposals" to hold Supreme Court justices to the same ethical standards as the rest of the federal judiciary, and Durbin had invited Roberts "or his designate" to take part.

"Testimony before the Senate Judiciary Committee by the Chief Justice of the United States is exceedingly rare, as one might expect in light of the separation of powers concerns and the importance of preserving judicial independence," Roberts wrote in his response to the invitation.

Durbin, in a subsequent statement, said: "Make no mistake: Supreme Court ethics reform must happen when the Court participates in the process or not." Any such effort at reform is unlikely to have enough support in Congress.

In response to Roberts' letter, Gabe Roth, of the judicial watchdog group Fix the Court, said in a statement: "Make no mistake: Roberts' statement is nowhere near an appropriate response to the ethical failures of the current Court."

"Roberts here is demonstrating a profound ineptitude to rise to the occasion, and our country is worse for it," Roth said.

The planned congressional hearings follow a series of news reports that raised questions about Justice Clarence Thomas' business dealings, and luxurious vacations that he and his wife took that were paid for by his friend, GOP mega-donor Harlan Crowe.

In his letter, Roberts noted that only two previous chief justices have testified before Congress, and in each case, Roberts said, the testimony concerned what he called "mundane matters."

Accompanying the letter was a 2 1/2-page statement of ethics principles and practices, which Roberts said all the current justices "today reaffirm and restate."

The document says that justices seek to abide by the code of conduct followed by the lower courts. That said, it makes a variety of exceptions to transparency rules in the name of security and for other reasons.

Since 1991 the justices have followed financial disclosure requirements on gifts, outside earned income, outside employment, etc. These reports are supposed to disclose, among other things, the justices non-governmental income, investments, gifts, and reimbursements from third parties. Roberts noted that the Judicial Conference has, just this year, tightened some of the disclosure requirements, for instance requiring disclosure of free airplane trips and other gifts from friends that in the past have been exempted.

Nonetheless, the ethics statement signed by all the justices says that "individual justices, rather than the court, decide recusal issues." Translation: There still is no group enforcement mechanism. As the ethics statement puts it, "If the full court or any subset of the court were to review the recusal decisions of individual justices, it would create an undesirable situation in which the court could affect the outcome of a case by selecting who among its members may participate."

Finally, the ethics statement makes quite a point of security, noting that justices are facing increasing threats, and that matters such as travel accommodations and disclosure may at times have to take a backseat to security. In other words, methods of travel and places where a justice might stay may remain hidden from view.

Durbin, for his part, said in a statement, "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." [Copyright 2023 NPR]