A state ballot measure to ban gay marriage in California is gaining momentum, with polls showing almost even odds of it passing after trailing by double digits a month ago.

In June, the state legalized same-sex marriages. The next month, Proposition 8, defining marriage as between a man and a woman, was put on the ballot for November. Initial polling showed that a majority of Californians were likely to vote against Proposition 8. A Sept. 18 poll by the San Francisco-based Field Poll found the measure losing 55% to 38% among likely voters.

But now the measure is favored 48% to 45% among likely voters questioned in an Oct. 17 poll by Survey USA of Verona, N.J. The poll’s margin of error, four percentage points, means the results were a statistical tie.

A group leading the fight against the measure, Equality for All, said this week that one of its internal polls shows Proposition 8 leading by four percentage points. The close results of that poll, too, may suggest a dead heat as the Nov. 4 election approaches.

“The outcome will be close because Californians are evenly divided on gay marriage,” said Mark Baldassare, chief executive of the nonpartisan Public Policy Institute of California in San Francisco. A new poll by the institute, due out late Wednesday, is expected to show a tight race. The measure needs a simple majority vote to pass.

Proposition 8 was initiated after the state’s Supreme Court said in May that a ban on same-sex marriage is unconstitutional, paving the way for the legalization of gay marriage in California starting June 17. Same-sex marriages are also legal in Massachusetts and Connecticut.

Read the full story from the Wall Street Journal.