The Cincinnati-based Campaign to Protect Marriage must collect 323,000 valid signatures to put the issue before voters in November. But a coalition of gay rights advocates could block the effort by tying it up in court or getting enough signatures tossed out.

A lawsuit filed this week in the state 10th District Court of Appeals argues that all petitions collected in the Cincinnati and Cleveland areas should be tossed out for a variety of reasons, including the fact that they do not contain a required summary of the amendment.

The amendment effort is already expected to come up at least 17,000 signatures short of the state requirement - a figure supporters think they can overcome by submitting more than 100,000 additional signatures.

But if the lawsuit is successful, it could eliminate more than 50,000 valid signatures from Hamilton and Cuyahoga counties, significantly increasing the signature deficit.

Donald McTigue, an election law attorney hired by opponents, said the lawsuit also names the secretary of state's office as a defendant in hopes that a ruling in his favor could invalidate signatures in all counties.

David Langdon, author of the amendment and attorney for the Campaign to Protect Marriage, called the lawsuit a "Hail Mary with no merit to it."

"They waited too long," he said, adding that such a challenge should have been brought forward when petitions were first submitted to the secretary of state's office in early August.

McTigue disagrees and will plead his case before a three-judge panel in Columbus on Monday.

McTigue also has filed legal challenges to petitions in 42 counties.

While most are pending, challenges in Hamilton and Washington counties have been dismissed. Amendment opponents won their challenge in Logan County, getting about 1,700 signatures tossed out.

The amendment would ban gay marriage, end domestic partner benefits offered by four state universities, and could affect legal agreements between unmarried couples.

E-mail jsiegel@enquirer.com