TALLAHASSEE -- Florida's marriage amendment continues to fall short of the support necessary for passage, according to a poll out today.

Amendment 2's fate will hinge on the one in 10 respondents who say they haven't decided how they'll vote -- or are unwilling to tell pollsters.

Mason-Dixon's poll of 625 likely voters on Thursday and Friday showed 55 percent support for Amendment 2, with 35 percent opposed. Constitutional amendments require 60 percent approval for passage, so the proposal will be determined by the 10 percent of respondents who said they hadn't yet made up their mind.

The proposal would define marriage as between one man and one woman. Florida statutes already ban homosexual marriage, but proponents of Amendment 2 say the prohibition needs to be in the constitution to protect against lawmakers or judges who could change that.

Opponents argue the proposal would threaten the benefits and rights of unmarried couples no matter their sexual orientation.

Amendment 2, put on the ballot by signature petition, has consistently polled below the 60 percent requirement for passage. The Mason-Dixon poll's margin of error is plus or minus 4 percentage points.

Brad Coker, managing director of Mason-Dixon in Florida, said similar ballot questions in other states have shown that undecided voters tend to vote in favor of the gay-marriage bans.

"It still has a chance to win approval," Coker said.

Floridians will decide on five other proposed amendments in voting that concludes Tuesday. None have enough support in Friday's poll to pass, but Coker said four of the five still have a chance at passage. Four of the five still have a quarter or more of respondents undecided.

Only Amendment 8, which would allow local-option sales tax for community colleges, seems doomed. Though Mason-Dixon last asked likely voters about Amendment 8 two weeks ago, at the time 47 percent were against it and 15 percent were undecided. The proposal then had 38 percent support.