Colorado State Senator Pat Steadman has said he will introduce a bill that recognizes gay and lesbian couples with civil unions, the Denver Post reported.

The openly gay Steadman, 46, who has been partnered for over ten years says he believes Coloradans will support civil unions.

The lawmaker said he expects the Democrat-controlled Senate to approve the measure. But passage in the Republican-controlled House appears less likely.

“I think that kind of bill would be of concern with the vast majority of the members of our caucus,” House Speaker-elect Frank McNulty, a Republican, told the paper.

Colorado voters in 2006 approved a constitutional amendment banning gay marriage.

Social conservatives say they'll oppose the bill.

“We could not support a law that undermines marriage, and that's exactly what civil unions do,” Jenny Tyree of Citizen Link, a group affiliated with Focus on the Family, said.

“This is a steppingstone to one thing only, and that's redefining marriage, and that has happened in other states.”

Vermont, the first state to approve civil unions, has since legalized gay marriage.

If approved, Colorado would join New Jersey and Illinois in offering the union. Illinois lawmakers recently approved a similar law and Governor Pat Quinn has promised he'll sign it into law. Hawaii lawmakers are also expected to debate the issue next year.