The US Supreme Court unveiled an ethics code on Monday following a series of scandals over lavish gifts and luxury vacations received by some of its justices.

The nine members of the nation's highest court are the only federal judges not explicitly subject to ethical oversight, and pressure has been mounting from Democrats in the Senate for them to adopt a code of conduct.

In a statement, the Supreme Court said the absence of a formal code had led to a "misunderstanding that the Justices of this Court, unlike all other jurists in this country, regard themselves as unrestricted by any ethics rules.

"To dispel this misunderstanding, we are issuing this Code, which largely represents a codification of principles that we have long regarded as governing our conduct," the court said.

"For the most part these rules and principles are not new," the court said. "The Court has long had the equivalent of common law ethics rules."

Adoption of the code comes some seven months after the non-profit ProPublica news outlet reported that Justice Clarence Thomas had accepted years of luxury travel trips from a billionaire Republican, including yachting in New Zealand and private jet flights across the globe.

ProPublica also reported in June that another conservative justice, Samuel Alito, had flown to Alaska in 2008 for a luxury fishing trip on a private jet owned by a billionaire hedge fund manager who later had cases before the court. 

Both Thomas and Alito have denied any impropriety.

The nine-page Code of Conduct, which was signed by all nine justices, requires them to "uphold the integrity and independence of the judiciary" and "avoid impropriety and the appearance of impropriety in all activities."

"A Justice should not allow family, social, political, financial, or other relationships to influence official conduct or judgment," it says.

The code also includes rules on acceptance of gifts and bars justices from speaking at events "sponsored by or associated with a political party or a campaign for political office."

Staunch conservative Thomas, the longest-serving justice on the court, went on one trip to Indonesia that alone was likely worth $500,000 — paid for by real estate tycoon Harlan Crow, according to ProPublica.

Crow has made more than $10 million in donations to Republican political groups, ProPublica said, including half a million dollars to a conservative lobbying group founded by Thomas' wife Ginni Thomas.