Supporters in the gallery of the House chanted "shame on you"directedat Republican House Speaker FrankMcNulty after he made the announcement. The gallery was cleared and the House adjourned for the night.
The bill appeared to be close to becoming law in Colorado earlier in the day after it passed out of the final committee on Tuesday afternoon and went to the House floor.
However, the debate before the second reading and vote on the bill never came upand the bill's supporters failed to get the vote in before midnight.
The House Appropriations Committee passed the bill around 5 p.m.
During the debate on the House floor, Republicans accused Democrats of trying to force a vote, while Democrats say Republicans filibustered and wasted the last hours of the day on lengthy debate over issues that were not pressing.
The sides could not agree, and Republican leaders used their majority power to stop the debate. They called a recess before 10 p.m. Gov. John Hickenlooper (D-Colorado) returned to the Capitol late Tuesday night in an effort to broker a deal to get the bill passed.
Hickenlooper is expected to weigh in on Wednesday on whether the legislature may enter a special session because the civil unions bill was one of 30 that remained unfinished on Tuesday night.
Around 11 p.m.,McNulty said the issue reached an "impasse" and the legislation was, for all intents and purposes, dead.
"We're willing to work with you to figure out a way to make sure that every bill tonight gets an up or down vote on it and I think that's fair and that's the Democratic process," Rep. Mark Ferrandino (D-Denver), one of the bill sponsors, said earlier in the night.
"There's not time to have a full debate and hearing on every single bill that's left to be heard in this assembly. There are approximately 30 bills that are left to be heard," Assistant Majority Leader Mark Waller (R-Colorado Springs) said.
The Appropriations Committee attached two amendments to the bill before passing it.
One of the amendments allows certain religious organizations, such as schools or hospitals, not to acknowledge civil unions.
The other allows providers of social services or mental services not to provide those services to people through civil unions if it conflicts with the organization's beliefs.
The issue divided House Republicans who have a 33-32 voting edge. Despite that, it appeared the bill had enough votes to clear the chamber.
The full House could have taken off the amendments, but if that happened the bill would have to be sent back to the Senate for approval.
Ferrandino attempted to take those amendments off on Tuesday night.
Lawmakers adjourn at midnight Wednesday and must take a final vote before then or the bill dies. The bill needed a preliminary vote on Tuesday night because it cannot have the second and third readings on the same day, according to state law.
The Senate had already approved the bill and Hickenlooper supports the bill and would sign it.
The bill could have marked a dramatic shift in a state that banned gay marriage in 2006. Democrats are concerned Republicans will use procedural tactics to run out the clock on the bill.
McNulty says Democrats turned the issue into a manufactured end-of-session crisis for political gain.
Supporters flocked to the Capitol steps to rally for the bill to be heard on Tuesday. The entire Democratic caucus from the Senate came out with the supporters to rally with them.
If it had passed, Colorado would have joined more than a dozen states that allow gay marriage or civil unions.
The legislation granted gay couples rights similar to marriage, including enhancing inherence rights, parental rights, and the ability to be involved in partner's medical decisions.
Under the bill, employers would not be required to extend the same benefits to the partner of employees in civil unions that they do to spouses. Civil unions would be available to both same-sex and opposite-sex couples under the proposed law.
The bill got over its first major hurdle last Thursday when it was passed by the House Judiciary Committee on a 6-5 vote. In that case, one Republican also joined Democrats to approve it. Rep. B.J. Nikkel (R-Loveland) voted for the bill this year. She changed her vote from last year, where the same committee defeated a similar bill.