PORTLAND – Citing free-speech protections, Maine’s highest court Tuesday struck down a state election law that triggered an ethics commission rebuke in a legislative primary race two years ago in Cape Elizabeth.

The statute requiring a candidate who uses an endorsement in political advertising to include explicit authorization from the endorser conflicts with the candidate’s First Amendment rights, the Maine Supreme Judicial Court said.

Michael Mowles’ opponent in the Republican primary complained about his ad, which included endorsements by U.S. Sens. Olympia Snowe and Susan Collins during a previous campaign.

The Commission on Governmental Ethics and Election Practices concluded that Mowles broke the law and fined him $1. Jonathan Wayne, the commission’s executive director, said he had no immediate comment on the supreme court’s unanimous decision.

After a Superior Court judge upheld the commission’s decision, Mowles appealed to the supreme court, which handed down its ruling nearly a full year after it heard arguments.

The supreme court agreed with the commission that Mowles’ use of the Snowe and Collins endorsements were unauthorized, but concluded that there was no apparent fraud because his campaign flier said in smaller type that the endorsements dated back to October 2004.

“American history cautions against governmental regulation of political speech. Absent that caution, in the guise of the most benevolent purposes, an incumbent government could restrict the free flow of information and debate in the public marketplace of ideas,” Chief Justice Leigh Saufley wrote.

The outcome was applauded by the Maine Civil Liberties Union, which took on Mowles’ appeal and argued his case before the Law Court.

“This ruling is a victory for all the people in Maine,” said Zachary Heiden, MCLU legal director. “The First Amendment gives voters, not the government, the right to approve or disapprove of candidate speech.”

The ethics complaint had been filed by Jennifer Duddy, who went on to defeat Mowles in the primary in House District 121 but lost the general election. Neither candidate is on the ballot this year.