"The highest court in the land should not have the lowest ethical standards.

Democratic lawmakers in the U.S. Senate on Tuesday called with legislation that would set new ethical standards for justices on the U.S. Supreme Court.

This comes amid revelations that Justice Clarence Thomas, one of the six conservatives on the bench, had reportedly received but never disclosed gifts and travel from a Texas billionaire and Republican donor.

Dick Durbin is the Democratic chairman of the Senate Judiciary Committee:

"Last month we learned about a justice who for years has accepted lavish trips and real-estate purchases worth hundreds of thousands of dollars from a billionaire with interests before the court. That justice failed to disclose these gifts, and has faced no apparent consequences under the court's ethics principles."

But Republicans sought to cast the effort to require greater disclosure from the justices as a left-wing plot to delegitimize a conservative court and its decisions.

Here's Republican and ranking committee member Lindsey Graham.

"We can talk about ethics, and that's great. But we're also going to talk about today of a concentrated effort by the left to delegitimize this court and to cherry-pick examples to make a point. [FLASH] This is not about making the court better. This is about destroying a conservative court. It will not work."

None of the nine justices appeared at the hearing, with Chief Justice John Roberts last week declining an invitation by Durbin for him to testify.

Supreme Court justices are not bound like other federal judges by the same code of conduct adopted by the broader federal judiciary. Other federal judges under that code must avoid even the "appearance of impropriety."

Witnesses invited by Democratic lawmakers told the panel Tuesday that gap meant a dearth of oversight and accountability.

Kedric Payne is a lawyer specializing in government ethics.

"There are four basic ethics provisions that exist in the executive and legislative branches, that do not exist in the Supreme Court. As a result the Supreme Court has the lowest ethical standards in government."

But Republican witnesses claimed that a proposed bill imposing ethics standards on the Supreme Court would be an unconstitutional imposition by one branch of government on another. Here's attorney Thomas Dupree:

DUPREE: "It is the Supreme Court, not the Congress, that has the prerogative under our constitutional structure to decide whether to adopt a code of conduct that governs themselves."

Two U.S. senators, independent Angus King who caucuses with Democrats and Republican Lisa Murkowski, introduced legislation on April 26 that would require the Supreme Court to create a code of conduct and appoint an official to review ethics complaints.

With Republican opposition expected, any such legislation faces an uphill battle in a divided Congress.