"We are examining the facts," said David Bookbinder, Washington legal director for the Sierra Club. "We certainly understand why there is a public uproar about this."

But Bookbinder said the group had not decided yet whether to move to ask Scalia to bow out of the case.

Cheney is being sued by the Sierra Club and Judicial Watch, a government watchdog group. The two groups want Cheney to release documents about White House contacts with the energy industry in 2001 but the vice president has appealed a judge's ruling ordering him to produce the documents.

In mid-December, the Supreme Court agreed to hear Cheney's appeal.

Several Democrats in the U.S. Congress have sent letters to Chief Justice William Rehnquist asking him to look into whether Scalia should recuse himself from the case.

"When a sitting judge, poised to hear a case involving a particular litigant, goes on vacation with that litigant, reasonable people will question whether that judge can be a fair and impartial adjudicator of that man's case or his opponent's claims," senators Patrick Leahy and Joseph Lieberman wrote to the chief justice.

When asked about the matter, a Supreme Court spokeswoman said Scalia was traveling out of town and could not be reached for comment.

But Scalia last month told the Los Angeles Times - which first reported the hunting trip - that he did not think he needed to recuse himself.

"I do not think my impartiality could be reasonably questioned," he was quoted as saying. He said "social contacts" between justices and senior government officials are not improper and likened it to attending the vice president's annual Christmas party.

Kevin Kellems, spokesman for Cheney's office, referred questions to Scalia's office. "Justice Scalia has addressed it. I would refer you to that," he said. Judicial Watch President Tom Fitton said his group would not ask for Scalia's recusal.

"Unless information comes out that they discussed the case, we don't see an issue here," Fitton said. "And certainly if they discussed the case, there would be no doubt that Scalia would recuse himself. We have no reason to doubt his integrity on the issue."

A date has not been set for oral arguments in the energy task force case.