The Minnesota House appears unlikely to approve a measure to bring now secret political spending into the sunshine this year, House Speaker Paul Thissen said on Tuesday.

"I think it would be very difficult to pass that bill this year because of opposition from certain interest groups," said Thissen, DFL-Minneapolis.

The measure, which had the strong backing of DFL Gov. Mark Dayton, would require groups that spend money on Minnesota politics to reveal their spending and donors, no matter what type of group they are.

Such undisclosed spending has grown in the state but, because much of it comes from political nonprofits and the ads avoid certain words that trigger disclosure, it currently need not be reported to the state's campaign finance agency. The measure is one of several designed to reveal more information about the influence over and conflicts of the state's politicians.

Chief sponsor of the disclosure measure, DFL Rep. Ryan Winkler said without the new law there are big loopholes "that these groups can drive truckloads of cash through."

But some -- particularly the influential National Rifle Association and Minnesota Citizens Concerned for Life -- believed the law would have wrecked havoc on the work they do to inform voters.

“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 in March.

Thissen started this year saying that he thought the House was ready to pass the disclosure bill and has said he personally supports it. But on Monday, he halted debate on the issue when Winkler brought the measure up on the floor, which speakers rarely do to members of their own party, and Tuesday he said he not gotten enough DFLers on board to pass the bill yet this year.

"We trying to get to that point, but we haven't been able to convince all of our members," Thissen said on Tuesday.

Winkler, of Golden Valley, said he will continue to push the measure next year, if he wins his seat again.