Proponents of Proposition 8, California's gay marriage ban, urged the Supreme Court to uphold the ban in their opening briefs filed Tuesday.

The 2008 voter-approved constitutional amendment put an end to the weddings of gay men and lesbians taking place in the state after the state Supreme Court legalized such unions.

“By adopting Proposition 8, the People of California demonstrated their belief that this matter is best resolved by the People themselves, not by their courts,” Charles Cooper, a lawyer for Protect Marriage wrote. “The Equal Protection Clause does not prohibit the People of California – or any state – from making this choice. To the contrary, it leaves them free to do what they are doing – debating this controversial issue and seeking to resolve it in a way that will best serve their families, their children and ultimately their society as a whole.”

Protect Marriage is the original sponsor of Prop 8. The group stepped up to defend the law in court after California's elected officials refused to do so.

“An animating purpose of marriage is to increase the likelihood that children will be born and raised in stable and enduring family units by their own mothers and fathers,” Cooper argues. “Because relationships between persons of the same sex do not have the capacity to produce children, they do not implicate this interest in responsible procreation and childrearing in the same way.”

The Supreme Court will hear oral arguments in the case in March and is expected to issue a ruling in June.