HELENA, Mont. (AP) — Montana Lt. Gov. Mike Cooney asked his fellow Democratic gubernatorial candidates Wednesday to limit outside spending and self-funding in the election by signing a pledge that one opponent’s campaign called a stunt that could hinder the party’s nominee in the November 2020 general election.

Cooney sent copies of the pledge to the other Democratic candidates before signing it himself at a news conference at the Capitol. He plans to follow the conditions even if none of the others sign it, though he said he doesn’t expect that to be an issue.

“Everybody’s going to have to agree to it, I just don’t know why they wouldn’t,” he said. “If everybody signs it, that sends a very clear message to outside groups that we don’t want your involvement, please stay away.”

Cooney’s pledge asks candidates to promise to donate to charity half of the value of any independent expenditure made by outside organizations, individuals or corporations that benefit their campaign. Independent expenditures are typically ad buys to influence elections made by groups without any knowledge or coordination by a candidate’s campaign.

Candidates who sign the pledge also promise to donate to charity 50 cents for every $1 they give to their own campaigns.

“Let’s reject dark money groups, let’s reject special interests, super PACs and the anonymous committees that take refuge in the shadows of a broken campaign finance system,” Cooney said. “And let’s reject self-financing. Having personal wealth shouldn’t be the only thing that qualifies you to run for public office.”

Cooney took in more than $250,000 during the last fundraising quarter, far more than House Minority Leader Casey Schreiner or ex-legislator Reilly Neill. Whitney Williams, a Missoula businesswoman and the daughter of former U.S. Rep. Pat Williams, launched her campaign after the last reporting deadline.

Campaign finance records show no independent expenditures have been made as of last month.