Two high-profile lawyers have collaborated on a brief to the Supreme Court, in which they argue that it should overturn not only Proposition 8, but all bans on same-sex unions in the US.

The Supreme Court is due on 26 March to take up the case of whether to overturn Proposition 8, which in 2008 added a clause to the Californian constitution stating that marriage could only be recognised by the state if it were between a man and a woman, causing widespread controversy.

A number of parties including state representatives and top lawyers have filed “amicus curiae” briefs giving their views on what they believe the court should do.

President Obama himself is deliberating whether to file a brief in favour of equal marriage before the deadline of 28 February.

Leading attorneys Ted Olson and David Boies, who have been at the head of the legal battle against Proposition 8 since 2009, filed a brief making a case for the Supreme Court to dispel not only Proposition 8, but all bans on marriage between same-sex couples in the US.

They argue: “Because of their sexual orientation — a characteristic with which they are born and which they cannot change — plaintiffs and hundreds of thousands of gay men and lesbians in California and across the nation are being excluded from one of life’s most precious relationships.

“They may not marry the person they love, the person with whom they wish to partner in building a family and with whom they wish to share their future,” they wrote.

They argue that Proposition 8 “denies gay men and lesbians their identity and their dignity; it labels their families as second-rate. That outcome cannot be squared with the principle of equality and the unalienable right to liberty and the pursuit of happiness that is the bedrock promise of America from the Declaration of Independence to the 14th Amendment and the dream of all Americans.”

Mr Olson said that they were also concerned about the effect the ban would have on the children of same-sex couples.

“There are nearly 40,000 children living in California households of gays and lesbians. This is about their rights, their equality and their families,” he said.

 In 2011 Mr Boies defended Judge Vaughn Walker, who made a decision to overturn Proposition 8 but faced criticism for not revealing he was in a relationship with a man at the time.