AUGUSTA, Maine (AP) — Maine's highest court could decide to weigh in on the constitutionality of a dramatic election overhaul approved by voters last fall, and parties on both sides of the issue faced probing questions by justices in a packed courtroom Thursday.

Ranked-choice voting allows Maine residents to rank ballot choices from first to last and ensures that the winner gets a majority. But there are questions of constitutionality, and the Maine Senate asked the Supreme Judicial Court to weigh in.

The court can issue non-binding, advisory opinions on important questions of law when a "solemn occasion" arises. It's unclear when justices will issue an opinion.

During oral arguments Thursday, justices asked whether such a profound change requires a constitutional amendment and whether providing such guidance would address questions the public may have such as how to vote and how to campaign.

If the court decides to weigh in, the issue boils down to how to interpret the Maine Constitution, which refers to certain offices being elected by "a plurality of the votes."

Nationwide, a dozen cities have adopted ranked-choice voting, and Maine voters became the first to endorse the system for statewide elections. The system will be used for races for governor, U.S. Senate, U.S. House, Maine Senate and the Maine House.

Supporters say the system ensures a candidate wins majority support while eliminating the impact of spoiler candidates or party extremists who lack centrist appeal. Critics say it's costly, less transparent and would create problems of its own like increased vulnerability to hackers.

Attorney Timothy Woodcock, who represents the Senate, said ranked-choice voting would mean a historic and costly shift from local, "transparent" control over vote-counting to a more centralized system overseen by the Secretary of State's office. Joshua Dunlap, a Portland attorney representing the House Republican caucus and the Maine Heritage Policy Center, argued voters "intended to change from a plurality system to a majority system."

"It's not about shaping legislation, asking the justices to advise or intrude on the legislative process," said Assistant Attorney General Phyllis Gardiner, who argued for Attorney General Janet Mills and Secretary of State Matthew Dunlap, both Democrats. "Is this statute unconstitutional as we believe it is? If so then the Senate has the opportunity now to propose amendments (to the constitution) and get it decided by voters in 2018."

Kilbreth said if the high court weighed in, it would become overly involved in the legislative process. He and Rachel Wertheimer, who argued for the League of Women Voters of Maine and Maine Citizens for Clean Elections, said ranked-choice voting doesn't violate the constitution because in effect, the winner would be elected by a "plurality."

"The Constitution is a living, flexible document," Kilbreth said, who also argued that "plurality just means the highest number" and that laws can create "huge changes" without needing to be incorporated into the Maine Constitution.

Wertheimer said justices must give weight to the fact that residents approved the initiative.