Even as members of Congress from Minnesota on Thursday demanded tougher rules for disclosure of political spending, business interests urged a federal judge in St. Paul to toss out a state law barring corporate advertising for candidates.

Anticipating a new era of freewheeling special-interest spending, Sens. Al Franken and Amy Klobuchar, both Democrats, said they want to ensure that the public can figure out where the money is coming from. They signed onto a bill that would slap new regulations on political expenditures by corporations and unions in federal elections.

The bill appears to lay down a marker in an election year in which Democrats will try to tie their Republican opponents to Wall Street and other corporate interests. The lawmakers said their goal is for the Senate to pass the new measure by July 4, to curb the flow of corporate money in the 2010 midterm elections.

In Minnesota, Rep. Ryan Winkler, DFL-Golden Valley, is pushing a measure at the Legislature to require corporations and unions to disclose spending over $5,000 within 48 hours.

All of the efforts are aimed at blunting the impact of a landmark U.S. Supreme Court ruling earlier this year that cleared the way for corporations and unions to spend unlimited money supporting or opposing candidates. That decision applied to federal elections but inspired efforts in Minnesota and elsewhere to overturn statutes barring similar spending in state races.

The Minnesota Chamber of Commerce asked U.S. District Judge Paul Magnuson to declare unconstitutional a state law prohibiting corporate political spending. Chamber lawyer Thomas Boyd told Magnuson that its members may want to advertise, use Internet social media or wage a phone campaign to influence races. Boyd sought an injunction against enforcement of the statute in the state's 87 counties. Magnuson took the matter under consideration.

While the U.S. Supreme Court ruling covers races for Congress, invalidating the state law would allow spending for every office from governor to city council. Expecting the state law to eventually be overturned, Common Cause president Mike Dean said Thursday he hoped Magnuson would wait until the Legislature crafted stricter disclosure rules.

"We don't have any laws to govern this new world," Dean said. Winkler's bill lacks Republican support in the House and Senate, and there has been no assurance that Gov. Tim Pawlenty would sign it.

In Congress, Franken and Klobuchar are joining Sens. Charles Schumer, D-N.Y.; Russ Feingold, D-Wis., and others in trying to impose tougher regulations. Republican leaders criticized the measure as an attempt by Democrats to gain an advantage at the fall elections and beyond.

The bill would require groups running political ads to disclose donors, including corporate donors. Corporate officials would have to appear on camera and say they "approve of this message," much as candidates do now.

It also would bar foreign-run corporations, government contractors and companies that receive federal support from running political ads and making other political expenditures. Franken, who sponsored the measure aimed at overseas corporations, said, "Minnesota's elections should be controlled by Minnesotans."

He has called the Supreme Court ruling "an incredible act of judicial activism," wiping out restrictions on corporate spending in elections.

Klobuchar said the decision "was further evidence that special interests have had too much influence in our political process for too long."

Pat Doyle • 651-222-1210