Every time allegations are made about ethical lapses on the Supreme Court, the same question is asked: Why, unlike federal judges in lower courts, do the nine justices not have a binding code of conduct?

It came up amid the furor over the conservative political activism of Justice Clarence Thomas' wife, Virginia "Ginni" Thomas, including her support for former President Donald Trump's efforts to overturn the 2020 election results.

It came up when conservative Justice Antonin Scalia went duck hunting with then-Vice President Dick Cheney when Cheney was involved in a case pending before the court.

It came up when liberal Justice Ruth Bader Ginsburg was heavily critical of then-Republican presidential candidate Trump during the 2016 election.

And it came up last week with questions raised about the legal recruiting job held by Chief Justice John Roberts' wife, Jane Roberts, in which she has worked with law firms that have cases before the court.

Until now, the justices have held firm, even though district court and appeals court judges are bound by a judicial ethics code. Among other things, it requires judges to "avoid impropriety and the appearance of impropriety in all activities." If judges breach the code, they can be investigated and reprimanded via a separate complaint process.

The justices say they follow the spirit of the code, introduced in 1973, but they have never formally adopted one of their own. There is also no procedure that allows for complaints to be investigated short of the drastic step of impeachment.

Pressure has repeatedly come from Congress, with Sen. Chris Murphy, D-Conn., set to re-introduce legislation on Thursday that would require the justices to adopt a code. Similar efforts in recent years have failed.

"It's a simple, nonpartisan solution to increase transparency, enforce accountability, and start to rebuild public confidence in the court," Murphy said in a statement.

The bill, like previous versions, would task the Judicial Conference of the United States, the policymaking body for federal courts, with issuing within a year of enactment a code of conduct applying to Supreme Court justices. It also contains a new provision that would authorize an ethics investigations lawyer who would have the power to enforce the code.

Murphy has more than 20 co-sponsors in the Senate, and companion legislation in the House of Representatives is set to be introduced by Rep. Hank Johnson, D-Ga.

The Senate Judiciary Committee is expected to hold a hearing on judicial ethics, a Democratic Senate aide said.

Earlier this week, the American Bar Association, a national group representing lawyers, also called for the justices to adopt an ethics code.

Roberts addressed the court's inaction on the issue in his 2011 end-of-year report on the judiciary, saying it was a "misconception" that the Supreme Court has more lax ethical standards than lower courts.

"All members of the court do in fact consult the code of conduct in assessing their ethical obligations," he said.

Any effort by Congress to intervene could raise constitutional questions because lawmakers would be meddling in the internal affairs of a separate branch of government. But the Supreme Court already follows recusal and financial disclosure rules that were adopted by Congress. The court, as Roberts noted in 2011, "has never addressed whether Congress may impose those requirements."

Supreme Court spokeswoman Patricia McCabe declined to comment.

Judicial reform used to be something of a bipartisan issue, but in recent years, with growing scrutiny - especially on the left - of conservative justices, including not just Thomas but also Justice Brett Kavanaugh after his contentious Senate confirmation, Republicans have become less likely to back legislative efforts. This has also coincided with the court's shift to the right, thanks to a 6-3 conservative majority made possible by Trump's three appointments.

In the wake of calls last year for Thomas to recuse himself from cases involving Trump because of his wife's involvement in efforts to overturn the 2020 election, Republican Senate Leader Mitch McConnell conflated various issues, characterizing Democratic calls for reform as "part of a years-long quest to delegitimize the court." He dismissed Democratic concerns as "spurious accusations about fake ethical problems or partiality."

Gabe Roth, executive director of Fix the Court, a nonpartisan court reform group, said he is trying to convince Republicans that ethical rules are not just targeting conservatives.

"That's just the way it is covered, unfortunately, in conservative media," he said.

If the Supreme Court were to voluntarily adopt a code of conduct, the first of what Roth hopes would be a whole series of reforms, "it would be an easy win" for the justices, he added.

Ethics experts have long pressed the justices to take such a step.

Their failure to do so "makes it look like they have something to hide," said Arthur Hellman, a professor at the University of Pittsburgh School of Law.

But Charles Geyh, a professor at Indiana University Maurer School of Law, noted that the court traditionally bristles at Congress ordering it around.

"In a less fraught political environment, this standoff could and should be ended by congressional leaders quietly conferring with members of the court and agreeing to stand down if the court takes on the task of adopting a code," he said