HELENA -- Montana's Republican U.S. Sen. Conrad Burns flipped his stance on a 2001 bill after he received a $5,000 donation from a Jack Abramoff client opposing the bill, records show.

The client hired Abramoff as a lobbyist to defeat the kind of bill Burns voted against. Before receiving the payment, Burns did not oppose an identical bill that unanimously passed the Senate in 2000, Senate documents show.

Burns, who is up for re-election next year, told Lee Newspapers Friday the campaign contribution had nothing to do with his later opposition to the bill. He said the vote happened so long ago, he couldn't remember why he opposed the measure. Burns said he may have initially not opposed the bill's unanimous passage because it was politically more expedient not to stand in the way of a popular bill.

"Any time you put a hold on a bill, you expend political capital,'' Burns said.

The Wall Street Journal and the Washington Post both have reported that Burns is among four lawmakers caught up in a U.S. Justice Department investigation into Abramoff and his lobbying activities. The papers cited anonymous sources. Burns representatives have said the Justice Department has never contacted the senator.

The 2001 bill dealt with labor and immigration controls in the Commonwealth of Northern Marianas Islands, a constellation of 14 islands between Hawaii and the Philippines that is controlled by the United States. It grew out of reports that many workers in the islands' garment industry were Chinese immigrants earning less than the U.S. minimum wage. Because the islands are a U.S. territory, their products could be imported into the United States with a "Made in U.S.A'' label.

In 2000, records show, the U.S. Senate took up a bill that would have broadened federal oversight of immigration and labor rules on the islands. The bill came before the Senate Energy and Natural Resources Committee, of which Burns served. The bill passed out of committee, records show. However, due to the way the vote was recorded, it is impossible to tell how any individual senator, including Burns, voted on the measure.

On the floor, the bill faced no resistance, passing by unanimous consent. Not one senator including Burns opposed it.

The Senate did not actually vote on the bill. Rather, senators agreed to pass it unanimously without taking a vote. Any one senator, including Burns, could have opposed the unanimous passage.

Burns said Friday that because there was not an actual vote on the bill, it's impossible to say that he definitely supported the measure.

"Not always can it be assumed that a piece of legislation that passes on unanimous consent can you definitely say, 'That's a yes vote,' '' Burns said.

The bill then went to the House, where it died in committee.

Senators proposed an identical bill in 2001.

That year, the Saipan Garment Manufacturers Association hired Abramoff as a lobbyist, records show. Saipan is one of the larger islands in the Commonwealth of Northern Marianas Islands.

Abramoff's lobby registration shows the association hired him to ''prevent enactment of legislation to impose federal control over local labor and immigration rules.''

The same document lists Shawn Vassell, Burns' former state staff director, as a lobbyist on the issue. Vassell worked for Abramoff at the Greenberg Traurig lobbying firm.

The association paid Abramoff $460,000 that year to defeat the bill, records show.

The Commonwealth of the Northern Marianas Islands also hired Abramoff in 2001 to defeat the bill. The Commonwealth paid Abramoff $1.1 million. Vassell was also listed as a lobbyist on the issue.

On April 20, 2001, a Saipan man named Eloy Inos donated $5,000 to Friends of the Big Sky, Burns' political action committee, federal campaign finance records show. Inos listed his employer as Tan Holdings.

Tan Holdings owns, among other things, garment manufacturing facilities on the Marianas Islands. It is a member of the Saipan Garment Manufacturers Association, according to the company's Web site.

On May 23, 2001, the bill again came before the Committee on Energy and Natural Resources for a vote. In an unusual move, Burns requested that each member's vote be recorded next to their names a so-called "roll call'' vote. Often times, such votes are recorded by voice only. On a voice vote, there is no record of how each member voted and it is impossible to tell how an individual senator voted by reading a transcript of the meeting.

Burns' roll call request meant that his vote would be a traceable part of the public record.

This time, Burns reversed course and voted against the bill. He was one of four committee members to do so.

The vote came one month and three days after Burns received the $5,000 donation.

Burns said he doesn't remember why he requested a roll call vote.

"I haven't a clue why,'' he said. "You're talking four or five years ago.''

The bill then passed out of committee, but the full Senate never acted on the measure, records show. The bill has never become law.

"Burns actually voted for the bill before he voted against it,'' said Matt McKenna, a spokesman for the Montana Democratic Party. "The only thing that happened in between is he got paid.''

The Montana Democratic Party already has run two television ads linking Burns to Abramoff in anticipation of his 2006 re-election campaign.

The Senate Indian Affairs Committee has also been investigating Abramoff for months on whether he swindled Indian tribal clients out of millions of dollars.

In 2003, Burns helped one of Abramoff's tribal clients, the Saginaw Chippewa tribe in Michigan, obtain a $3 million congressional grant to build a school. Because of its Indian gambling, the tribe is one of the richest nationally and makes annual $70,000 payments to each member.

The Montana senator has denied any wrongdoing. Burns, who headed a Senate subcommittee overseeing the grants, said he pushed for the grant to the Saginaw Chippewa tribe at the urging of Michigan's two U.S. senators, both Democrats.

Burns received $136,500, more than any other lawmaker, from Abramoff's tribal clients from 2001 and 2004, a Bloomberg News database showed.