Members of the commission that oversees Maine’s campaign finance laws unanimously endorsed a proposal Thursday that aims to shine light on national political organizations playing a growing role in the state’s elections.

The proposal from the state ethics commission would require any organization that contributes more than $100,000 to a Maine political party, a political action committee or a ballot question committee to identify the organization’s top five donors, among other things. Commission members said while there are no guarantees the proposal will survive the legislative process, it attempts to increase donor transparency following some of the most expensive election cycles in state history.

“It is an issue that needs to be addressed in some way. This is a good way to raise it and to start,” said Margaret Matheson, chairwoman of the Maine Commission on Governmental Ethics and Election Practices.

Out-of-state organizations funneled tens of millions of dollars this year into campaigns in Maine this year to legalize marijuana, expand gun background checks, increase the minimum wage and fill the 2nd Congressional District seat. The spending shattered multiple records but also highlighted Maine’s status as a lower-cost venue for organizations to wage electoral battle on issues with national implications.

But those organizations frequently do not disclose their donors, making it difficult for Maine residents to know who is seeking to influence their vote.

Under current law, state campaigns and political action committees, or PACs, are required to disclose their donors. Yet those donors are often simply other PACs with anonymous donors of their own.

The proposal from the ethics commission staff, which won support from all five commissioners Thursday, would require organizations contributing more than $100,000 to file reports listing the five largest donors during the past year, as well as names and contact information for officers, the federal tax status of the organization and a certification attesting that the organization did not raise money specifically for the Maine campaign.

Those donors could be individuals or other organizations, underscoring the challenge of shedding light on campaign funders.

“My sense is enough folks are sick of what’s happening with our referendums now that it is worth discussion in the Legislature,” said commissioner and former lawmaker Richard Nass of Acton. “I’m not sure what the ramifications of these things are but that is the right place to bring the discussion. And I think part of our job is to get those thoughts over there to see what they want to do with them.”

All five of the ballot questions on Maine’s November ballot received donations from out-of-state organizations, but three in particular were largely bankrolled by national organizations. Everytown for Gun Safety, a gun control group founded by former New York City Mayor Michael Bloomberg, donated nearly $5.3 million to the unsuccessful Question 3 campaign to require background checks prior to private gun sales. The National Rifle Association, on the other hand, funneled roughly $1 million to Question 3 opponents.

Likewise, the campaign to legalize recreational use of marijuana received $2.2 million from an organization called New Approach PAC while the National Education Association donated $2.4 million to the campaign to increase education funding through a 3 percent tax surcharge on those earning $200,000 or more. And national groups donated millions of dollars to the campaigns on both sides of the aisle working on state legislative campaigns.

It is unclear how lawmakers will respond to the proposal. The Legislature rejected a more sweeping donor transparency proposal from the ethics commission in 2015 following the previous year’s costly elections.

The proposed bill would go to the Legislature’s Veterans and Legal Affairs Committee for consideration, although lawmakers are under no obligation to act on it.

The commission won a years-long legal battle with the National Organization for Marriage over the group’s refusal to identify the people behind its donations to a political action committee fighting same-sex marriage in Maine. In that case, the commission successfully argued that NOM should have filed with the state as a ballot question committee because it was fundraising for Maine’s 2009 referendum over same-sex marriage. Ballot question committees are required to disclose donors.

But a national organization that donates to a Maine campaign from its so-called “general fund” – made up of generic donations not solicited for a Maine campaign – does not currently have to disclose donors.

The ethics commission’s executive director said he could not rule out a constitutional challenge of the proposal, although he noted that California has a more stringent reporting requirement on its books. The specter of a legal battle still hung over the commissioners’ discussion, however.

“We’ve heard this from a number of sources: People want to know where is this money coming from and who is behind this ‘dark money,’ ” said Matheson, the commission chairwoman. “But I also want to be respectful of the fact that we don’t want to be enacting something that won’t pass a good constitutional muster.”

Maine Citizens for Clean Elections, a nonprofit that advocates for greater transparency and supports Maine’s public campaign financing system, said it supported the ethics commission proposal.

“These large contributions – often originating outside of Maine – play an increasing role in shaping our elections and influencing the outcomes,” Robert Howe with Maine Citizens for Clean Elections wrote to the commission. “Yet many of these contributions are made by entities with unfamiliar names and whose interests and background are obscure to the general public. It is very difficult for the public to assess the messages paid for by this money because the public lacks good information about the unique interest and possible motivations of the people and entities making these contributions.”