The pair have lost their court battle for the right to enter into a civil partnership.
Claim was rejected by the Court of Appeal in London.
Rebecca Steinfeld and Charles Keidan argued they were discriminated against because civil partnerships are not available to people of the opposite sex.
They oppose traditional marriage because they regard it as a “patriarchal” institution. Speaking outside court, Steinfeld said they were “deeply disappointed” by the ruling.
Mr Keidan, 40, said he and his partner were “determined to go on” with their appeal, taking the case to the Supreme Court if the government didn’t act.
“Opening civil partnerships to all is fair, popular and will be good for families and children across the country,” he said.
There are over three million mixed-sex couples who are cohabiting, with two million dependent children. This is the fastest growing family type, but these couples lack legal and financial security.”
The judges said there was a potential breach of their human rights, but the government should have more time to decide the future of civil partnership.