Sources of political spending that are now secret could be forced into the light of disclosure if Gov. Mark Dayton has his way.

“This is about people’s right to know who is trying to influence the outcome of elections and how much money they are investing to do so,” Dayton said in an interview with the Star Tribune. “I strongly support that.”

The governor’s backing makes it more likely that starting with this year’s elections, Minnesotans would be able to track the sources of all politically tinged mailings and ads that come out before Election Day.

The spending on such campaigning has grown to unprecedented heights, but some big spenders are not required under current law to tell the public about their work to change ­voters’ minds.

“It’s really polluting and distorting the process,” Dayton said.

Ads and mailers that do not use key phrases like “vote for” or “vote against” and which do not come from registered groups like political action committees or political parties are not required to have their spending disclosed. So the messages, largely from political nonprofits, can freely bash or support candidates so long as they don’t explicitly tell Minnesotans how they should vote.

“You could run essentially the same kind of ad, have the same effect, run it anytime and still not be subject to any kind of disclosure,” said Gary Goldsmith, executive director of the Minnesota Campaign Finance and Public Disclosure Board.

Goldsmith said the state has little way of quantifying how much political spending goes unrevealed. One study in Michigan from a group that advocates for more disclosure found that at least $18 million worth of television ads were not disclosed in 2012 because they fell under the rubric of “issue ads.”Sen. Jim Carlson, DFL-Eagan, has tried to calculate the cost of political mailings sent in 2012 to voters in his state Senate district. He has estimated that groups spent more than $50,000 to thwart him without telling the public about the spending or who contributed the cash. That estimate is in addition to the nearly $300,000 in independent spending aimed at supporting his Republican opponent or opposing Carlson that was subject to public disclosure.

“Money is wielding so much power these days,” Carlson said. “I think it’s real important that the public knows how much elections are costing and from where the money is ­coming.”

What does a group say?

If the measure Dayton supports becomes law, it would matter less what kind of group is spending the money and more what they say about politics. The new requirements would broaden the definition of a political ad, saying, in essence, that if a reasonable person would view an ad, mailing or billboard as a political ad, then it is a political ad. In addition, if a group targets voters 30 days before a primary election or 60 days before a general election, it must publicly report its spending and its major donors — even if the group is a nonprofit or a corporation.

About half of states now require political groups to reveal some version of that type of spending. Last year, Minnesota joined the other half of states in getting a failing grade on the pro-disclosure Center for Public Integrity’s scorecard for revealing too little about independent spending on elections.

Dayton, a DFLer, made clear to the Star Tribune that he would make an exception to his dictate that election-related bills should have bipartisan support to win his signature. The disclosure bills have not attracted any Republican support, but Dayton said: “I’ll sign that bill, happily and proudly.”

Passage isn’t guaranteed

The governor’s support could prove critical.

“We are not going to spend time passing bills the governor won’t sign,” said Rep. Ryan Winkler, DFL-Golden Valley, sponsor of the House version.

Despite the governor’s backing, the measures — in slightly different versions in the House and the Senate — have no guarantee of passage.

Sen. Scott Newman, R-Hutch­inson, said he agrees in principle with greater disclosure. But the Senate bill is too vague, he said, and would give the Campaign Finance Board too much power to determine what is a political purpose.

The Minnesota Chamber of Commerce also is leery of the disclosure bills. Laura Bordelon, the chamber’s vice president for advocacy, said that the chamber supports “full and fair disclosure,” but that “we do not support further restrictions to our ability to advocate on behalf of issues or candidates.

Perhaps more powerfully, both the National Rifle Association and Minnesota Citizens Concerned for Life, a nonprofit organization and the state’s largest anti-abortion organization, oppose the measures, and they have asked their supporters to do so as well. The NRA and the MCCL have bipartisan backing in the Legislature.

“These fatally flawed bills pose a grave risk to freedom of speech in Minnesota and impose excessive regulatory burdens on political and commercial interests,” the NRA told supporters this month.

The MCCL has told legislators that the bill is too far-reaching and that it would have “a significant chilling effect on MCCL’s ability to engage in grass-roots issue advocacy.” In a letter, the group’s lobbyist Andrea Rau said it would score the votes on the issue. That means that legislators for whom a perfect voting record opposing abortion is important would see their grades slip if they vote for the disclosure bill.

That opposition may sway the House, whose members are all up for re-election this year.

House Speaker Paul Thissen, DFL-Minneapolis, said he is not yet sure if he can wrangle enough votes to send the bill to the governor. He said he is personally talking about the issue with Democratic representatives to make that happen.

“I don’t know if we have the votes yet or not,” Thissen said.