AUGUSTA — The National Organization for Marriage has lost another round in its attempt to hide the identities of donors to a successful 2009 referendum campaign that reversed Maine’s marriage equality law.

On Tuesday, the Maine Supreme Judicial Court refused the organization’s request for a stay that would have enabled it to delay complying with a state ethics board ruling that it must file a report identifying the sources of the $2 million that NOM gave to the referendum drive.

NOM has mounted a relentless legal battle to conceal the names of its donors, saying that they could be subjected to harassment or economic reprisals by supporters of gay marriage, and that the organization’s fundraising efforts would suffer.

Last year, the Maine Commission on Governmental Ethics and Election Practices imposed a $50,250 fine on NOM, the nation’s largest organization opposed to gay marriage, because it failed to register as a ballot question committee or file campaign activity and donor disclosure reports.

In April, a Maine Superior Court upheld the ethics commission decision to fine NOM and require the group to list its donors.

The decision Tuesday sets the stage for NOM to proceed with an appeal before the Supreme Judicial Court that will determine whether the ethics commission erred when it ruled that NOM should have filed as a ballot question committee. Tuesday’s ruling means the group can’t withhold names of donors to the 2009 campaign while the appeal process plays out.

Jonathan Wayne, director of the ethics commission, said it wasn’t immediately clear whether the ruling will require additional action by the commission. He said NOM has paid its fine – a record amount – and filed as a ballot question committee, under protest. He said the ruling by the state’s highest court means that NOM now should file a campaign finance report.

Wayne said the court’s decision also indicated that the organization wouldn’t likely win its appeal.

In its ruling, the court wrote that NOM’s efforts to block donor disclosure had not been successful in either state or federal courts.

“After reviewing the motion record and carefully weighing the four criteria, we conclude that, because there clearly is no substantial possibility that NOM will succeed on the merits of its claims, a stay is not warranted under applicable principles of law and equity,” the ruling stated. “The circumstances underlying the commission’s decision occurred almost six years ago, and the decision has successfully withstood federal and state court challenges during that time. NOM now asks us to decide many of the same issues and has failed to sufficiently show that it has a likelihood of succeeding on the merits. Accordingly, we deny NOM’s motion for a stay pending appeal.”

Attorney General Janet Mills, whose office represents the ethics commission, applauded the ruling and called on NOM to release donor names.

“The time has come for them to finally comply with state law like everyone else,” she said. “The people of Maine have a right to know who is paying to influence our elections.”

Stephen Whiting, a Portland attorney hired by NOM’s legal team, said he had not had a chance to read the ruling. However, he said he was in the process of preparing to file the appeal of whether NOM is indeed a ballot question committee, as the ethics commission ruled.

Joseph Vanderhulst, an attorney with the Indiana-based law firm Act Right Legal Foundation, which is handling NOM’s appeal, said Tuesday that the group had not discussed what it would do if it lost its appeal with Maine’s highest court. Theoretically, he said, the group’s only remaining legal recourse would be with the U.S. Supreme Court.

In June, the Supreme Court ruled that the Constitution requires that same-sex couples be allowed to marry no matter where they live.

NOM gave more than $2 million to the $3 million referendum campaign to overturn the marriage equality law that the Legislature passed and Gov. John Baldacci signed. The law never took effect.

Brian Brown, NOM’s executive director, was an operating officer of Stand for Marriage Maine, a Maine-based ballot question committee that registered with the state. The ethics commission members argued that Brown’s dual role allowed the organization to shield its donors and skirt Maine’s donor disclosure law.

The ethics investigation cited bank statements and campaign literature to show that the organization used its nonprofit status to draw donations earmarked for the Maine referendum – a violation of Maine election law.