A lesbian couple are asking a court to rule that an amendment to a US state constitution banning same-sex marriage is unconstitutional.

Kate Burns and Shiela Schroeder argues that the voter-approved amendment is religious in nature.

They are due to appear in court this week charged with trespassing. The couple were arrested in September last year.

Ms Schroeder, 43 and Ms Burns, 44, staged the sit-in protest in the Wellington E Webb Municipal Building, when they were refused an application for a marriage licence from the Denver Clerk and Recorder Office.

The couple, who have been together for five years, took Rev. Mike Morran, their local minister from Denver’s First Unitarian Church with them.

Rev. Morran said:

“I am proud to stand on the side of love in support of Kate and Sheila.

“From a church point of view, marriage is a sacrament and the state should stay out of it. This civil right – the freedom to marry – should apply to all citizens.”

The couple were arrested when the office closed for the day and issued with citations for trespassing.

They were released without bail soon after.

In November 2006 Colorado voted to ban same sex marriages by adjusting the constitution so that marriage is only recognised if it is between a man and a woman.

“The right to marriage is fundamental,” Mari Newman, the couple’s attorney, told the Rocky Mountain News.

“The government can’t be telling us who we can and cannot marry.”