(CNN) -- Same-sex marriage became legal in Maine on Wednesday as Gov. John Baldacci signed a bill less than an hour after the state legislature approved it. "
I have come to believe that this is a question of fairness and of equal protection under the law and that a civil union is not equal to civil marriage," said Baldacci, a Democrat.
But he raised the possibility that the residents of the state would overturn the law, saying, "Just as the Maine Constitution demands that all people are treated equally under the law, it also guarantees that the ultimate political power in the State belongs to the people."
Three other states -- Massachusetts, Connecticut and Iowa -- allow same-sex marriages. Vermont has passed a law making gay and lesbian marriages legal that takes effect in September. New Hampshire lawmakers are close to passing a similar bill.
On Tuesday, the Washington City Council voted to recognize same-sex marriages from states that allow those unions. Mayor Adrian Fenty has indicated that he will sign the measure. It will become law if Congress fails to overturn the measure during a 30-day review period.
A slim majority of Americans are against legal recognition for same-sex marriage, CNN polling found last month.
Fifty-four percent of adults questioned in an April 23-26 nationwide CNN/Opinion Research Corp. poll said that marriages between gay or lesbian couples should not be recognized as valid, while 44 percent said they should be considered legal.
The survey's sampling error was plus or minus 3 percentage points.
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