WASHINGTON, D.C. - With the U.S. Supreme Court reaffirming the rights of corporations to donate unlimited amounts of money, Minnesota's restrictions on corporate donations could hang on a pending appeals court ruling.

Two advocacy groups and a business challenging the Minnesota law say the state's limits reach beyond the Supreme Court's intent.

On Monday, the nation's highest court struck down Montana's 100-year-old ban on corporate money in politics, a ruling consistent with the Citizens United decision that paved the way for unlimited corporate spending in federal elections as long as the money is independent of the campaign it is intended to help.

In response to that ruling, Minnesota's campaign finance law was revised by the Legislature in 2010 to allow for unlimited corporate contributions.

But the state also requires donors to funnel those contributions through political action committees that must file disclosure reports, a condition that quickly drew a legal challenge.

Two advocacy groups -- the Minnesota Taxpayers League and Minnesota Citizens Concerned for Life -- and St. Paul based-Coastal Travel Enterprises argue that the requirement violates the Citizens United ruling.

A panel of the U.S. Eighth Circuit Court of Appeals upheld the law in May 2011, but the full court vacated that ruling months later. The full appeals court heard the case in St. Louis in September, but has yet to issue a decision.

James Bopp Jr., an Indiana-based attorney who represents the advocacy groups and the travel company, doesn't expect the appeals court ruling to completely strike down Minnesota's law.

"Not directly," said Bopp, who has led challenges to campaign finance laws nationwide. In Minnesota, he said "We're challenging the definition of a political committee."

The struggle over disclosure rules is popping up in states beyond Minnesota, said Mike Dean, executive director of Common Cause Minnesota, a group that advocates for open government rules.

The Supreme Court decision to turn "a blind eye toward the tsunami of corporate money that's flooding the system" means that disclosure is the new front line for campaign finance conflict, Dean said.

In the Supreme Court majority opinion on Citizens United, Justice Anthony Kennedy wrote that "prompt disclosure of expenditures can provide shareholders and citizens with the information needed to hold corporations and elected officials accountable for their positions and supporters."

But during oral arguments on the Minnesota law before the federal appeals court, Bopp argued that Minnesota's requirement that organizations contribute through a political fund infringes on free speech.

"The requirement ... is un- duly burdensome," Bopp said.

Before the Citizens United case landed before the Supreme Court, Bopp represented the nonprofit corporation in its initial battle with the Federal Election Commission over attempts to air a documentary critical of then-presidential candidate Hilary Clinton during the 2008 election season.

Corey Mitchell is a correspondent in the Star Tribune Washington Bureau. Twitter: @StribMitchell