AUGUSTA, Maine — The Maine Senate, after lengthy floor debate, passed a bill Thursday that significantly alters clean election laws for publicly financed legislative candidates.

Some feel the changes put the Maine Clean Elections Act in jeopardy and others vowed to fight, possibly through a citizen’s initiative.

“We’re going to keep our options open,” said Andrew Bossie of Maine Citizens for Clean Elections. “Maine people have supported clean elections and while this bill doesn’t kill it, it certainly weakens it.”

Last, year, the U.S. Supreme Court ruled that the matching funds provision in clean election laws was unconstitutional. Matching funds are triggered when a privately funded candidate spends more money than a publicly funded candidate. Without them, a private candidate could spend significantly more than a public one, which some feel creates an inequity.

Because of that ruling, Maine lawmakers were forced to draft a bill that removed all matching funds references from the Maine Clean Election Act. LD 1774, which brings Maine into compliance with the federal court ruling, was first approved by the Veterans and Legal Affairs Committee in January.

Without matching funds, clean candidates now receive only upfront money, which amounts to less than $4,000 for House races and about $18,000 for Senate races.

Some lawmakers feel those totals are too low, especially in contested elections. Without a viable replacement that attempts to level the playing field for private and public candidates, critics believe the future of clean elections is in jeopardy.

On Thursday, lawmakers offered amendments to LD 1774 on the Senate floor, including two from Sen. Roger Katz, R-Augusta and several from Sen. John Patrick, D-Rumford.

One of Katz’ amendments sought to bump up the lump sums that would be distributed to clean candidates. There would be no funds for uncontested primaries. House candidates would get $1,500 for a contested primary and $4,000 for the general election. Senate candidates would receive $6,000 for a contested primary and $23,000 for the general. Katz’ amendment also would have doubled the amount of seed money contributions candidates can receive.

Patrick, through his amendments, proposed more upfront money in both House and Senate races. But more importantly, he wanted to include a “requalifying” option that would allow clean candidates to receive more money if they gather more small donations.

Each amendment was defeated.

When the unamended bill came up for a final vote in the Senate, it passed 18-15.

“We were comfortable all along passing a bill that just dealt with the matching funds,” said Sen. Debra Plowman, R-Hampden.

The clean elections bill still requires approval of the House, where another narrow vote is expected. Many legislative candidates, particularly those who face a primary in June, likely will be closely watching the final vote.

House Speaker Robert Nutting, R-Oakland, urged the House to pass the bill.

“When Maine voters approved this law more than a decade ago, they envisioned leveling the playing field for candidates who lacked the financial means to run for office. It was never intended to provide an open-ended flow of taxpayer money to pay for partisan political campaigns,” he said.

In 2010, roughly 80 percent of those elected to the Legislature ran as clean candidates, but many feel that the law today bears little resemblance to the spirit of what voters passed 16 years ago.

Democrats said the “do nothing” approach weakens Maine law because it allows privately financed candidates to use outside spending. They also feared that gutting the law will deter some candidates from running if they feel like they don’t stand a chance.

“This could be the beginning of the end for clean elections,” said Sen. Phil Bartlett, D-Gorham, who during testimony Thursday called the bill a “missed opportunity” and lamented a federal court system that is “doing everything it can to put money back into politics.”

Bartlett said the climate in Washington, D.C. — especially since the Citizens United case that ruled corporations and unions are people when it comes to campaign contributions — has been poisoned by special interests. Some fear it might give more prominence to political action committees, which are not subject to donation limits.

Bossie said that was precisely why 60 percent of Mainers approved the Maine Clean Election Act in 1996, paving the way for House and Senate candidates to receive public dollars for their campaigns if they forgo private donations.

But Republicans said the clean elections act has done little to keep money out of politics.

Plowman also said it was hypocritical for Democrats to decry the influence of outside money. She pointed out that Equality Maine spent hundreds of thousands of dollars recently to champion a same-sex marriage initiative supported by Democrats and that the group has donated liberally to Democratic candidates.

“I’ve always been a traditional candidate and I’ve never spent what my opponents have spent,” Plowman said. “But I’ve done pretty well.”