Fresh revelations about a shooting trip taken by US Vice-President Dick Cheney and a Supreme Court judge are fuelling renewed allegations of impropriety.
Cheney has refused to comment on the affair
Justice Antonin Scalia accompanied Mr Cheney, an old friend, on a duck-shooting trip to Louisiana in January.
The Los Angeles Times says they travelled aboard one of the presidential jets, Air Force Two.
Mr Cheney is a defendant in a case currently before the Supreme Court over his refusal to grant access to records.
Justices regularly withdraw from cases where a conflict of interest is perceived.
But in this case, Justice Scalia has declined to do so, saying: "I do not think my impartiality could reasonably be questioned.
"Social contacts with high-level executive officials (including cabinet officers) have never been thought improper for judges who may have before them cases in which those people are involved in their official capacity, as opposed to their personal capacity," he told the Los Angeles Times.
Mr Cheney himself has not commented.
Mr Cheney and Justice Scalia flew to Louisiana on 5 January, where they spent several days at a duck-hunting camp owned by Wallace Carline, a friend of both men and a Democrat, the local sheriff was quoted as saying.
They were said to have hunted that afternoon and the next morning before rain interrupted their activities.
The Los Angeles Times, which originally broke the story, now alleges they made the controversial trip aboard Air Force Two, at taxpayers' expense.
One of the other men in the group has described it as a "strictly social" occasion, and ordinarily, critics say, they would not question their right to maintain a friendship.
But Mr Cheney is due to appear before the Supreme Court in a case brought by the environmental group the Sierra Club and a legal watchdog, Judicial Watch.
They are appealing against the decision of a district court which upheld a White House refusal to release details of meetings and contacts by Mr Cheney's energy task force.
Those details were first requested by the investigative arm of Congress in February 2002 after the Enron scandal.
Two Democrat senators, Patrick J Leahy and Joseph Lieberman, have written to Chief Justice William H Rehnquist to question the propriety of the men spending extended lengths of time together, reported the New York Times.
However, the chief justice said the ethics of such situations were covered by federal laws, and it was largely down to justices themselves to decide whether it is proper to hear a case.
But these fresh revelations have worried Bill Allison, of the Center of Public Integrity.
"It does raise the level of closeness a little bit higher," Mr Allison told the Washington Post.
"It makes it seem more like Cheney was courting Scalia."