Gay marriage opponents in Maryland have promised to put a law that legalizes such marriages up for a vote if it is approved by lawmakers.

“Every state that has ever voted on the definition of marriage has voted in favor of defining marriage as the union of a man and a woman,” Peter Sprigg, senior fellow for Policy Studies at the Family Research Council (FRC), told Washington-based 630 WMAL News.

The bill has gained majority support in the Senate, and Governor Martin O'Malley has promised to sign the bill into law, giving backers reason to hope. But opponents could block the measure in the Senate with a filibuster.

Sprigg, who earlier testified against the measure at the Statehouse, told the radio station that there are consequences to allowing gay and lesbian couples to marry.

“We'll see schools being used as places to indoctrinate children into affirming homosexual relationships,” he said. “We see a slippery slope towards efforts to redefine marriage to include polygamous relationships.”

Sprigg's group is also active in the campaign to ban gay marriage in Minnesota.

On MSNBC's Hardball last year, Sprigg called for the re-criminalization of gay relationships. FRC President Tony Perkins has since denied that his group sanctions the criminalization of gay sex.