HELENA, Mont. (AP) — Montana Gov. Steve Bullock signed a first-of-its-kind executive order Friday to require many state government contractors to report their political contributions, even those to so-called "dark money" groups that don't have to disclose donors under federal law.

Bullock said the measure is an example of how states can bring transparency to spending by groups classified as social welfare organizations under the federal tax code. Those dark money groups' influence increased dramatically after the 2010 U.S. Supreme Court's Citizens United ruling that allowed unlimited corporate election spending.

Bullock said he hopes other governors will follow his example, as they have with a net neutrality executive order he signed in January. New York and New Jersey governors have signed their own versions of Bullock's order requiring state contractors to not interfere with internet speeds or content.

"Just like net neutrality, this is (an) area where state governors can make a meaningful, meaningful difference," he said.

Bullock, who is exploring a possible presidential run in 2020, first announced the new policy during a speech Tuesday at the liberal think tank Center for American Progress in Washington, D.C. Critics accused Bullock of trying to manufacture news to raise his national profile.

"He's using this executive order to try to garner media attention to his own presidential campaign that no one is talking about," said Matthew Monforton, an attorney who is challenging a separate Bullock-backed state law that reformed campaign disclosures.

Bullock deflected questions about his national political ambitions, except to say issues like dark money, free internet and public lands are "not just important to me, but to regular folks all across the West and the country."

Under the executive order, all companies submitting bids for contracts valued at more than $25,000 for services or $50,000 for goods must disclose two years' worth of political spending if that spending exceeds $2,500.

The requirement will take effect Oct. 1, and current contractors are exempt. Bullock's chief legal counsel, Raphael Graybill, estimated that the new requirement would apply to between 500 and 600 contracts a year.

Bullock passed the 2015 Disclose Act through the Republican-led state Legislature under the similar principle of requiring more transparency by all groups that spend money to influence state elections. That law has been upheld by the 9th U.S. Circuit Court of Appeals, though two challenges, including Monforton's, are still pending.

Bullock said that his executive order, like the Disclose Act, complies with the Supreme Court's Citizens United decision because that ruling called for increased transparency of corporate spending in elections.

Anita Milanovich, an attorney who is also suing to strike down the Disclose Act, said that was a distorted interpretation of Citizens United, and that the court's call for increased disclosure applied only to groups expressly advocating for the election or defeat of a candidate.

The Montana law requires disclosure of any group that simply mentions a candidate in advertising without that express advocacy, and the executive order takes the law a step further by targeting donors to those groups, she said.

"If you give money to someone who mentions a candidate, you can't be eligible to be considered for a contract unless you tell us about it," Milanovich said. "I think it is kind of begging for that prospective challenge."

The governor effectively dared someone to file a legal challenge to his executive order.

"Look, I'd certainly welcome some dark money group to challenge it because I think it's not only consistent with the law but consistent with what Montanans hope to know about who's trying to influence their elections," Bullock said.

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This story has been updated to correct that Bullock's speech in Washington was Tuesday, not Wednesday.