Denver Mayor Michael Hancock is expected to inaugurate Colorado's civil union law at the stroke of midnight on May 1.

One Colorado, the state's leading gay rights advocate, is organizing the event to take place in Denver's Webb Building.

The 2-hour event will be held in the building's atrium, where Hancock will preside over some of the state's first ceremonies.

Hancock said he is “honored to take part in this historic event, uniting committed couples who were for too long excluded from the same benefits and protections provided to their fellow citizens. At midnight May 1, our great state will bring down some of the senseless walls that have divided us and state in one voice: 'Everyone matters.'”

Colorado lawmakers approved the law earlier this year on the third try. A 2006 voter-approved constitutional amendment defining marriage as a heterosexual union prevents lawmakers from considering extending full marriage to gay and lesbian couples.

Civil unions are also legal in Hawaii, Illinois, New Jersey, Delaware and Rhode Island. Rhode Island lawmakers, however, on Wednesday approved a marriage law, and Illinois and Delaware are considering doing the same.