Bob Cummins, who has donated more than $3.5 million to Minnesota Republican causes, is telling allies he has had it with Republicans in the Minnesota Legislature and will not give their campaigns any cash this year, according to multiple sources.

Cummins, CEO of Plymouth-based Primera Technology, is reportedly frustrated over legislators' failure to approve a "right-to-work" constitutional amendment that would limit union power. At least 21 states have such restrictions.

A pillar of GOP financing in years past, Cummins' support could be especially critical for Republicans, who have seen contributions drop off as their money troubles mount.

Senate Majority Leader Dave Senjem, R-Rochester, said he has not talked personally with Cummins recently but would not be surprised if he withheld contributions. "He was pretty tied in to the right-to-work issue, and I think that was his main legislative priority. I don't think I would expect a lot of help out of him given that we didn't advance that," Senjem said.

Cummins, who seldom talks to reporters, did not respond to repeated requests for comment.

Beyond being a major source of financing for legislative campaign committees, Cummins has also served as a "thought leader" among conservative givers. As he backs away, others could join him.

His frustration could compound Republicans' money problems and hinder their attempt to hang on to their legislative majorities. The state Republican Party has been digging out from a huge debt and may not be able to offer legislative campaigns much financial help.

"He has a lot of the same base frustration that activists have," said one source who knows Cummins well and has spoken to him and his staff recently.

The source said Cummins' thought is: "If you are not supporting the same political agenda that I'm supporting, then why should I support you?"

Big bucks

Cummins, who made his fortune in specialty printing equipment used by most of the nation's Fortune 500 companies, has been the single biggest donor to Republican House campaigns in recent years. He gave $865,000 to House Republicans between 2006 and 2011 alone. Senate Republicans, who took over that chamber for the first time in generations in 2010, also have gotten significant contributions from Cummins.

"His absence would be felt, no doubt, in caucus fundraising," said former House Minority Leader Marty Seifert.

Last year, the House caucus reported just over $1 million in donations. Cummins' $125,000 gift was the largest. The Senate reported $856,000 in fundraising. Cummins and his wife, Joan, donated $125,000 to the Senate Victory Committee.

Besides his contributions to the party campaigns, Cummins has given heavily to the Freedom Club, a group that supports conservative lawmakers. That group, established in 1995, has raised about $2 million since 1998, with Cummins contributing more than a quarter of that.

The Freedom Club, which has spent about $1.8 million on past legislative races, had $280,550 on hand earlier this month. Cummins, several sources said, might increase his giving to the club. That group can pick which Republicans candidates to back. The caucuses are not designed to pick campaign favorites. Cummins can also give to individual candidates' campaigns, as he has in the past, although the size of those contributions is limited by law.

"Instead of being against Republicans, he and others will be more choosy early in the process," Seifert said.

To be sure, both legislative campaign efforts have other big givers, although none at Cummins' level of generosity.

"We have all kinds of donors," said House Speaker Kurt Zellers, R-Maple Grove. Zellers said he has not talked to Cummins recently. Neither Zellers nor House Majority Leader Matt Dean professed knowledge of Cummins' displeasure.

Stanley Hubbard, who has given almost $200,000 to the House caucus and about $50,000 to the Senate caucus over the past decade, was more open about his frustration over the Republicans' failure to push a right-to-work amendment.

"I would like to have seen that get on the ballot or have a law pass offering freedom of choice," said Hubbard, chairman of Hubbard Broadcasting. But he did not say he would withhold contributions.

Never had the votes to pass

Senjem said that despite the high interest of Cummins and others in such an amendment, legislative support just wasn't there.

"Honestly, we didn't have the votes," Senjem said. "There were not 34 votes or frankly anywhere close to 34 votes." That's the number needed in the Senate to place a constitutional amendment on the ballot.

Charlie Weaver, executive director of the Minnesota Business Partnership, said while being a right-to-work state might help job growth, putting it on the ballot this year would have been "unwise from a political perspective."

"Not this year, not this election. At some point? Sure," Weaver said.

Neither the partnership nor other influential business groups pushed the proposal.

Unions would have pounced on Minnesota had it passed and poured tens of millions of dollars into the state, turning the state's elections into a madhouse, several Republicans said.

"I believe that, frankly, the caucus leaders were intimidated by opposition coming into this election," Thompson said.

The sole hearing the Legislature had on the issue in March was nearly drowned out by chanting union protesters. Unions have begun sending mailings into the districts of legislators who supported the move.

If Republicans manage to keep control of the Legislature, the issue may be back. "It will certainly be something we look at revisiting," Senjem said.

Rachel E. Stassen-Berger • Twitter: @rachelsb