A Colorado gay couple has filed a lawsuit seeking to overturn the state's constitutional ban on same-sex marriages.

Dr. Rebecca Brinkman and Margaret Burd filed the lawsuit Wednesday in Adams County District Court after they say they were denied a marriage license earlier the same day. Colorado voters outlawed gay marriage in 2006.

This year, Colorado passed a same-sex civil unions law. But Brinkman and Burd's attorneys argue civil unions are inferior to marriage and more like a business relationship. The attorneys say Colorado's ban is unconstitutional and cite the U.S. Supreme Court ruling from June that invalidated part of the Defense of Marriage Act

Brinkman and Burd have been in a relationship for 34 years.