DENVER  —  A $500,000 donation by Republican beer baron Pete Coors (search) to his own Senate campaign has triggered a new federal law that eases fund-raising restrictions for his Democratic opponent.

Called the "millionaire amendment," the law was designed to make sure wealthy candidates did not have too much of an advantage in election campaigns.

Coors spokesman Cinamon Watson confirmed Sunday that Coors had made the donation Friday.

"Extreme environmentalists and lawyers have dumped millions in to attack Pete Coors. I think all Coloradans would agree that when you are attacked in that manner you have to defend yourself," Watson said.

A spokesman for state Attorney General Ken Salazar (search), Coors' opponent, said Coors already had donated about $550,000 to the campaign, and Friday's donation put him well over the threshold limit of $571,000.

"When times get tough for American families they can't bail themselves out with million-dollar checks," said Salazar spokesman Jim Carpenter. "But, in a last-ditch effort to rescue his struggling campaign, Peter Coors is now trying to buy this election with an 11th-hour infusion of his personal wealth."

Carpenter said donors, previously limited to $2,000, could now give $6,000 to Salazar's campaign, which has raised about $7.5 million.

Watson said Coors had raised $7 million. The latest poll of registered voters showed Salazar with 47 percent and Coors with 43 percent; the margin of error was four points.

So far this campaign year, only a few general election candidates have triggered the spending rule, the limits of which vary depending on the population. The Coors' campaign notified Salazar when it surpassed the limit, Carpenter said.

Candidates in House races in Missouri and Ohio and a Senate race in Maryland have put enough of their own money into their campaigns to allow their opponents to make use of the new rule.