As activists prepare for what is expected to be one of the costliest amendment campaigns in recent history, state campaign finance officials are rethinking guidelines on how donations are disclosed.

The Minnesota Campaign Finance and Public Disclosure Board met Tuesday to hear arguments on whether it should revoke a 14-year-old opinion that allows corporations to make donations to ballot campaigns without revealing their own donors.

A change could have a major impact on the role national heavyweight nonprofits like the Human Rights Campaign and the National Organization for Marriage play in Minnesota over the next 17 months. The two sides are gearing up over a 2012 ballot question that would ask voters to legally define marriage in the state Constitution as being between a man and woman. It would solidify an existing legal ban on same-sex marriage.

For-profit corporations like Target may not experience much change, however, because they rely on business revenue rather than donors.

Amendment supporters said that requiring disclosure could scare off potential donors.

Tom Prichard, president of the nonprofit Minnesota Family Council, said that donors could be subject to "physical violence, economic threats or harassment, property damage" if their names are disclosed. "Forcing organizations like ours to make their donors public would have a chilling effect on political speech [and] free speech," Prichard said.

Opponents of the amendment did not testify at Tuesday's hearing, but are watching the matter closely. Donald McFarland, who leads the coalition opposing the measure, said his organization has no official position. "Everyone's watching and waiting for the advice," McFarland said.

The state already requires a higher level of disclosure from groups that donate money to sway the election of a candidate.

But Josiah Neeley, an Indiana-based attorney representing the coalition supporting the amendment, testified that the two situations should not be viewed equally.

"You can't corrupt a ballot question," Neeley said. "It's not a person, it's a legislative measure."

Mike Dean, executive director of the watchdog group Common Cause Minnesota, said corruption is still a possibility -- especially if amendment campaigns have an impact on the broader elections.

"I really think the public has a right to know about who's funding this political speech," Dean said. "One of the ways that we can prevent that corruption ... is to bring campaign contributions into the sunlight."

Similar fights have already played out in other states that waded into the gay marriage debate.

Neeley is representing the National Organization for Marriage (NOM) in a lawsuit to protect the names of its donors in Maine. NOM successfully fought to repeal the state's same-sex marriage law in a 2009 referendum.

Neeley, who said repeatedly in his testimony that corporations are "legal persons," said there is a "serious possibility of litigation" if Minnesota revokes the opinion.

Advisory opinions have no legal authority, but political groups view them as the Campaign Finance Board's interpretation of the law. The board pushed bipartisan legislation this session requiring more disclosure from corporations that give to ballot measures, but the bill never got a final vote.

Prichard said the timing of this recent push is curious. "We're just concerned that it would come up after 14 years. What's changed?" he asked.

Gary Goldsmith, executive director of the Campaign Finance Board, said in a memo that the board has requested clarification from the Legislature several times dating back to 2002.

Board members asked questions but did not express concrete opinions on the issue. They delayed a vote until their next meeting on June 30, so that new disclosure guidelines will be drafted in the event that they revoke the opinion.

Eric Roper • 651-222-1210 Twitter: @StribRoper