AUGUSTA, Maine (AP) — Supporters of Maine's new ranked-choice voting law vowed Tuesday to fight a bill approved by lawmakers to delay, and possibly repeal, the voter-approved system.

Maine last year became the first state in the nation to approve statewide ranked-choice voting, which allows voters to rank candidates from first to last rather than voting for just one candidate.

Supporters say it ensures winners have broad support. But justices of Maine's highest court said in an advisory opinion that the system runs afoul of the Maine Constitution for some elections.

The Maine Legislature voted Monday to delay implementing the ranked-choice voting law for all elections until December 2021. Ranked-choice voting would then be repealed unless the state constitution is amended to explicitly allow the system.

Critics say the system isn't ready to be implemented next year in the largely rural state where many communities still hand-count ballots. Supporters of ranked-choice voting warned they'll challenge lawmakers who voted to delay the citizens' initiative and promised to fight for the 52 percent of last November's voters who supported the initiative.

"At the end of the day, the special interests and some politicians in Augusta don't like change," said Kyle Bailey, campaign manager for the 2016 ranked-choice voting referendum, on a Tuesday radio appearance on WVOM-FM. "It makes them nervous. They've been elected under an old system, and they're worried how a new system will treat them."

Bailey said a constitutional mechanism called a people's veto could prevent a delay and allow ranked-choice voting to be used in 2018 races.

Republican Gov. Paul LePage, an opponent of ranked-choice voting, has 10 days to veto or sign the bill approved Monday before it becomes law without his signature. Once it becomes law, ranked-choice voting supporters must then collect roughly 61,000 signatures to freeze it.

It would then be up to Maine voters to decide in a general election whether the Legislature's delay of ranked-choice voting should become law.

Democratic Secretary of State Matthew Dunlap said his office has begun planning how to roll-out statewide ranked-choice voting. But he said his office needs more funding and direction from lawmakers.

Dunlap said state officials had long warned advocates that the ranked-choice voting referendum would clearly clash with a section of the Maine Constitution that says winners are to be determined by a plurality.

The Legislature failed to pass a separate bill to institute ranked-choice voting for federal races and primaries for statewide office. Lawmakers have also lacked votes to start the process of amending the Maine Constitution to explicitly allow ranked-choice voting for general elections for the Legislature and governor.

Democratic Sen. Bill Diamond, a former Secretary of State, said he supported a delay because it would be "irresponsible" to leave the voting law alone and open the state up to possible litigation. He said Maine needs more time to work out ranked-choice voting's complexities, like what would happen in a recount.

"For us to put this mother of all nightmares on local clerks, volunteers and ballot clerks would be unreasonable, unfair," he said.