MADISON, Wis. -- The U.S. Supreme Court's decision that corporations can spend freely to support or oppose candidates is sure to have an impact in Wisconsin.

In a 5-4 decision, the U.S. Supreme Court overturned a more than 60-year-old ban on corporation spending, saying that Congress can not prohibit free speech, even by a corporation or union.

The decision means companies can now spend millions on issue ads to support or oppose candidates.

The ruling released on Thursday could thwart an attempt by lawmakers and state regulators to limit political spending by special interest groups that have become a major force in the state.

Just this week, the state Senate approved a bill that would require such groups to disclose their donors and abide by certain fundraising limits. Its supporters acknowledged the high court could wipe out the restrictions with its ruling.

The decision removes limits on independent expenditures that aren't coordinated with candidates' campaigns but leaves in place a prohibition on direct contributions to candidates from corporations and unions.

"So they went ahead and changed the campaign finance laws of our country. They are now letting corporations and unions use their treasuries, (and) your money when you buy toothpaste, now to run ads about candidates that you may not believe in," said Sen. Russ Feingold, D-Middleton.

Wisconsin also has a ban on corporation campaign spending that has been in place since 1905. The state Government Accountability Board said it's not sure how this will affect the law as well as a bill passed Tuesday by the state Senate that would also regulate issue ads.

The decision means that so-called "soft money" ads paid for by third-party groups could flood television sets this year.

"A simplistic answer is this is going to lead to a lot more money in politics, a lot more money on the air in terms of television advertising," said Ken Goldstein, a political scientist at the University of Wisconsin-Madison.

Feingold said he believes the decision allowing corporations to spend freely to support or oppose candidates is a terrible mistake.

"I think it's a disaster for our political process. I think if it isn't corrected by appropriate legislation, if we can do that, that the average person's voice will be even more drowned out and our society will be even more dominated with pharmaceutical companies, Wall Street, the insurance industry, everyone who is winning right now. The average person is going to lose," Feingold said.

Goldstein said those companies might run ads or contribute to political groups that will.

"I'm someone who actually thinks the more money in politics, the more advertising in politics, the more voices heard in politics is a good thing," Goldstein said.

Either way, it means more ads will be run, which Goldstein said could expand the political playing field in Wisconsin.

"We've only had one competitive race, the race up in the Fox River valley; it's been competitive the last couple years. The other races have not been competitive," Goldstein said. "Does the ability of groups to jump in with more money perhaps expand the playing field and make Ron Kind's seat a more competitive race than we would have thought in other circumstances?"

Wisconsin also has a ban on corporation campaign spending that has been in place since 1905. The state Government Accountability Board said it's not sure how this will affect the law as well as a bill passed Tuesday by the state Senate that would also regulate issue ads.