AUGUSTA, Maine — The National Organization for Marriage, the anti-gay marriage group that helped defeat Maine’s same-sex marriage law in 2009, may be fined more than $50,000 and ordered to reveal its donors, after an ethics investigation released Monday found that it violated the state’s campaign finance law.

Investigators with the Maine Ethics Commission said that the National Organization for Marriage’s failure to register as a ballot question committee and file campaign finance reports while playing a central role in the referendum was a “significant violation of the law.”

They also recommended that the commission order the group to file campaign finance reports with the state reflecting contributions and expenditures in support of the referendum.

“Maine people deserve to know who is funding political campaigns to influence their vote,” the report said.

NOM said Monday that the investigation’s findings were wrong and maintained that it fully complied with Maine law. The commission will consider the issue at a May 28 hearing and the organization said it will appeal if Maine rules it must pay the fine and submit a report.

NOM gave nearly $2 million to Stand for Marriage Maine, a political action committee, representing 64 percent of the PAC’s total expenditures, the report said.

State law requires groups to register as ballot question committees if they raise or spend more than $5,000 to influence a state ballot question.

Same-sex marriage became legal in Maine after a second referendum in 2012.

Investigators found that NOM received enough contributions through email solicitations that discussed the group’s efforts to fight the law in Maine to qualify as a ballot question committee.

The report also said that NOM members had “critical leadership roles” in the campaign and made that clear to donors. Brian Brown, then-executive director of NOM, was one of three members of the committee that led the Stand for Marriage Maine PAC.

NOM has been fighting in Maine courts to keep its donor list secret for several years, arguing that revealing it could have a chilling effect on contributors.

NOM contends that none of the contributions were earmarked specifically to fight Maine’s gay marriage law and says it returned all contributions made by those who tried to designate them for the state’s referendum.

The group, which has fought same-sex marriage laws across the country, says that it’s being targeted by Maine despite the fact that several groups on the other side of the issue — like the Human Rights Campaign, GLAD and the Maine People’s Alliance — took similar actions.

“This is a witch hunt. It’s an attempt to go after a group like NOM because of its position on marriage,” said Brown, now president of the Washington, DC-based organization.

Investigators wrote in a response to the group that all of the organizations mentioned by NOM, except for the National Gay and Lesbian Task Force, formed a ballot question committee or a Maine PAC.

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