A heterosexual couple in London plan to challenge the ban on opposite-sex civil partnerships, by filing an application at the capital's Islington Registry Office.
Tom Freeman and Katherine Doyle say the denial of civil partnerships to heterosexual couples is "discriminatory and perpetuates legal inequality."
"We don't like the institution of marriage. We would much prefer a civil partnership. It is time there was legal equality in both civil marriage and civil partnerships," said Mr Freeman and Ms Doyle.
They will be giving notice of their intention to form a civil partnership at 10.30am, on Tuesday 24th November 2009 at Islington Registry Office, Islington Town Hall, Upper Street, London.
Freeman said:"We think the 'separate but equal' system which segregates couples according to their sexuality is not equal at all. All loving couples should have access to the same institutions, regardless of sexuality. There should be parity of respect and rights".
Doyle added: "Just as gay couples should be able to have a civil marriage, civil partnerships should be available to straight couples who don't like the institution of marriage."
Under UK law, same-sex couples are banned from civil marriage and heterosexual couples are banned from civil partnerships (called civil unions in the US).
The couple are backed by human rights campaigner Peter Tatchell of OutRage!, who will join them on 24 November when they give notice of their civil partnership at Islington Registry Office.
Tatchell commented: "The ban on heterosexual civil partnerships is heterophobic. It is disciminatory and offensive. I want to see it ended, so that straight couples like Tom and Katherine can have the option of a civil partnership.
"I applaud their challenge to this unjust legislation. In a democratic society, we should all be equal under the law. The ban on same-sex civil marriage and on opposite-sex civil partnerships is a form of sexual apartheid - one law for straight couples and another law for heterosexual partners. Two wrongs don't make a right," he said.