With Illinois state lawmakers poised to consider a marriage equality bill in the lame duck session that begins Wednesday, Catholic bishops and other advocates of “traditional” are taking a new approach: same-sex marriage simply violates natural law.

“Marriage comes to us from nature,” said Chicago’s Cardinal Francis George, in a recent interview with the Chicago Tribune.

“That’s based on the complementarity of the two sexes in such a way that the love of a man and a woman joined in a marital union is open to life, and that’s how families are created and society goes along. … It’s not in our doctrine. It’s not a matter of faith. It’s a matter of reason and understanding the way nature operates,” he said.

But marriage equality advocates say the Church’s renewed effort to highlight natural law is a clever but disingenuous appeal to the masses.

“On sexual ethics, nature is neutral,” said Bernard Schlager, executive director of the Center for Lesbian and Gay Studies in Religion and Ministry at Pacific School of Religion in Berkeley, Calif. “We’re moral beings. We may look to nature for some aspects of how we are in our lives, but we answer to a higher standard. Sexual behavior is an expression of human love.”

Chief sponsors of the bill, Sen. Heather Steans (D-Chicago) and Rep. Greg Harris (D-Chicago) said they are close to securing enough support to bring the marriage bill up for vote, but won’t do so unless they are confident it will pass the current General Assembly.

George acknowledges that there is some “inevitability” to the bill’s introduction, but said he’s dismayed that natural law largely has been left out of the public debate.