The Obama administration threw its support behind a broad claim for marriage equality on Thursday, and urged the Supreme Court to rule that voters in California were not entitled to ban same-sex marriage there.

In a forceful argument, the administration claimed that denying gay couples the right to marry violates the Constitution’s equal protection clause. It said that Proposition 8, the state’s ban on same-sex marriage, should be subjected to “heightened scrutiny” — a tough test for any law — and stated flatly that “Proposition 8 fails heightened scrutiny.”

That argument is similar to the one made in the administration’s brief in a second case before the Supreme Court concerning the Defense of Marriage Act of 1996, which the administration has also asked the court to declare unconstitutional.

The latest brief, filed late Thursday, does not, however, ask the court to declare such bans unconstitutional nationwide; instead, it focused on Proposition 8, which was approved by voters in 2008 and is before the court in this case. That law was passed by a voter initiative just months after the state’s Supreme Court ruled that same-sex couples could marry. The brief notes that opponents of same-sex marriage in the California case have argued that the state offers, through the equivalent of domestic partnerships, a marital state in all but the name.