A landmark U.S. Supreme Court ruling Thursday stripping away restraints on corporate political spending in Minnesota and other states sets the stage for a new and bigger barrage of campaign advertising.

By a 5-4 vote, the court overturned two of its own decisions as well as the decades-old law prohibiting companies from funding their own candidate ads. The court said the ads are free speech, protected by the First Amendment.

"It's a game changer," said Josh Winters, executive director of Minnesota Public Interest Research Group (MPIRG), a nonprofit group often associated with liberal causes.

"In Minnesota, as elsewhere, we're going to see ... chaos break out," said Steven Smith, a political science professor at Washington University in St. Louis, Mo., who closely follows Minnesota politics.

The decision, expected to apply to unions as well, threatens state campaign finance laws across the country. That includes Minnesota, where corporations are barred from spending money on ads that specifically target candidates.

Businesses and unions now can give money to Political Action Committees (PACs), which in turn buy ads. Thursday's ruling clears the way for unfettered future spending from corporate coffers on ads, with candidates and causes pressing companies for money.

"It's potentially huge in congressional races," Smith said. "How is a 3M, a Cargill, a Medtronic going to see this? They're going to be under substantial demand to get involved."

Extending First Amendment rights to corporations is "profound," said former Federal Election Commission Chairman Michael Toner, a former Republican National Committee lawyer and adviser to Sen. John McCain, one of the principal authors of the 2002 campaign finance law. "It has the potential to reorder the campaign finance system."

Minnesota laws could be void

The full effect in Minnesota may not be known until someone challenges the state prohibitions in court, but the outcome of such a fight seems clear.

"In all likelihood, it will eventually result in these bans being lifted in the state," said Mike Dean, head of Common Cause in Minnesota.

Democratic attorney Marc Elias, Sen. Al Franken's top recount lawyer, said the effects in Minnesota may be felt immediately. "There isn't any analytical reason why this wouldn't apply to [Minnesota's] gubernatorial race," he said. "Corporate independent expenditures are now a constitutional right."

Ben Ginsberg, who went up against Elias as former Sen. Norm Coleman's recount attorney, said in a memo Thursday that the ruling could reduce political parties to "bit players" and hamper candidates' ability to control their message.

"Unless the laws change, the political party as we know it is threatened with extinction," wrote Ginsberg. Limits on the amounts candidates and parties can accept remain intact.

At least one local group welcomed the opinion.

"Minnesota businesses are regulated by legislation and legislators, and to forbid businesses from participating in the discussion has always been unfair," said Mike Franklin, elections policy director for the Minnesota Chamber of Commerce.

Others view the decision more darkly.

"We're never going to be able to compete with that kind of money in politics," said Winters, of MPIRG, a student-run group which has advocated for environmental and consumer causes. "It's going to dwarf any of what advocacy, union or non-profit groups can pull together."

Organized labor will be free to operate with fewer restrictions as well, but may be unable to match the full financial clout of corporate America. "There's no evidence that they [unions] have untapped wealth to spend," said Michael Malbin, executive director of the Campaign Finance Institute.

At the State Capitol, lobbyists are already envisioning a higher cost of doing business.

"It's going to get more expensive operating around here," said John Apitz, a veteran lobbyist.

Effect on downballot races

Legislative races that have been relatively low-cost and low-radar could change too.

"If, say, a corporation takes an interest in a state Senate race where it has direct interests, you could see money going into that race," said Hamline University law Prof. David Schultz.

One DFL legislator, Rep. Ryan Winkler of Golden Valley, said he will propose legislation that would require greater disclosure, making contributions easier to track.

Some analysts say it remains to be seen how many American companies will choose to get directly involved in political campaigns.

"Most for-profit organizations don't want to get involved in explicit candidate advocacy, because you're going to alienate half of your customer base," Malbin said.

While the decision could be a setback for reform advocates, they're not going quietly into the night. Malbin said the 2008 elections showcased the power of the Internet to generate small donor contributions. Future reform efforts may shift to expanded public funding rather than spending limits, he said.

"We can accomplish much of what people want to accomplish by building up from the bottom rather than trying to squeeze from the top," Malbin said.

Staff writers Bob von Sternberg and Rachel Stassen-Berger contributed to this report. Pat Doyle • 651-222-1210 Kevin Diaz • 202-408-2753