ST. PAUL, Minn. -- Barack Obama's presidential campaign has modified a request for money after a Minnesota official questioned whether it constituted an illegal raffle.

In a letter on the campaign's Web site, campaign manager David Plouffe tied the solicitation to the announcement that Obama will deliver his nomination acceptance speech at Denver's 76,000-seat Invesco Field at Mile High.

The Web site had previously offered supporters who donated at least $5 to the campaign a chance to win a free trip for two to the Democratic National Convention.

But Nick Kimball, an Obama campaign spokesman in Minnesota, says the request was modified so that a campaign donation was not required to win the trip.

Tom Barrett, the director of Minnesota's Gambling Control Board, says he had asked the state Department of Public Safety to look into whether the solicitation violated Minnesota gambling laws. Only nonprofit charities may conduct raffles in Minnesota.