A last-ditch effort by Colorado's governor to give gay couples rights similar to married couples in the state has failed.
Republicans rejected civil unions legislation during a special session that Governor John Hickenlooper called to tackle the issue.
Civil unions would let partners make medical decisions for eachother and enhance their parental and inheritance rights.
The bill had enough support to clear the House during the regular session and get to the Democratic governor's desk.
But Republicans refused to bring it up for a vote before a key deadline.
Mr Hickenlooper then brought politicians into a special session to reconsider what he called a "fundamental question of fairness and civil rights".
A Republican-controlled House committee voted down the bill along party lines.