The nation’s first federal trial on whether a ban on same-sex marriage is constitutional is set to begin Monday in San Francisco.

U.S. District Judge Vaughn Walker will preside over a two-week trial on a lawsuit in which two couples claim that California’s ban on same-sex marriage violates their federal constitutional rights to due process and equal treatment.

The measure was enacted by state voters in 2008 as Proposition 8.

The couples’ lawyers argued in a recent court filing that the initiative “is an irrational, indefensible and unconstitutional measure.”

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