A proposed constitutional amendment to ban gay marriage in Michigan failed Monday to win certification that would put the issue before voters in November.

The Board of State Canvassers deadlocked along party lines on whether to certify more than 464,000 signatures in favor of the amendment. Supporters needed only 317,757 valid signatures.

Two Democrats on the board voted against certification, while two Republicans voted for it.

Eric Doster (search), an attorney for a group that collected the signatures, accused the Democrats of ignoring their legal duty, and vowed an immediate challenge in the courts.

"We'll let the real judges decide now," Doster said.

Democrat board member Doyle O'Connor (search) said he is concerned the amendment's wording would mean employers cannot provide benefits to same-sex partners. He also said it could violate equal-protection laws and prohibit churches from deciding whom to marry.

"There comes a point when we have to say, `No, this doesn't and can't fly,'" he said.

Doster countered that O'Connor's concern about same-sex benefits isn't an issue because the state cannot affect contracts between two parties.

The amendment would define marriage as between a man and a woman. Gay marriage is already banned in Michigan law; opponents want language in the constitution to protect against judicial decisions or legislative initiatives.

Voters in at least 11 states will decide this fall whether their states' constitutions should forbid gay marriage.