Two senators have written Chief Justice William Rehnquist (search) to raise concerns about Justice Antonin Scalia's (search) impartiality in a case that involves the White House's energy task force.

Scalia went on a hunting trip to Louisiana with Dick Cheney (search), a longtime friend, shortly after the court agreed to review a lower court's decision that required White House to identify members of the vice president's task force.

Scalia has said there is no reason to question his ability to judge the case fairly.

But in their letter, Democratic Sens. Joe Lieberman of Connecticut, a presidential candidate, and Patrick Leahy of Vermont questioned whether the court can disqualify a justice who declines to withdraw from a case. The lawmakers asked if the court has issued any guidelines about accepting gifts or travel.

"When a sitting judge, poised to hear a case involving a particular litigant, goes on a vacation with that litigant, reasonable people will question whether that judge can be a fair and impartial adjudicator of that man's case," the senators wrote.

Scalia also had dinner with Cheney in November, two months after the administration asked the justices to overrule the lower court.

A court spokeswoman, Kathy Arberg, could not confirm whether Rehnquist had received the letter Thursday.