Colorado lawmakers approved a bill on Tuesday to legalize same-sex civil unions, and the state's Democratic governor, who has already indicated his support, was expected to sign the measure into law.
The Colorado House Democrats said the measure would provide benefits, protections and responsibilities to gay and lesbian couples similar to those granted heterosexual pairs.
The measure, which passed by a 39-26 vote in the state House of Representatives, had already been approved by the state Senate.
"This bill is about three simple things, it's about love, it's about family and it's about equality under the law," Colorado House Speaker Mark Ferrandino, an openly gay Democrat and a sponsor of the bill, told fellow lawmakers.
The measure, once it is signed into law, would make Colorado the 18th state to approve either civil unions or gay marriage, according to the Colorado House Democrats. On Monday, lawmakers in the House rejected a number of Republican-sponsored amendments to the bill.