Proponents of same-sex marriage argued in federal court Thursday that a California ban on gay marriage was motivated by hostility toward gays and lesbians, rendering the law unconstitutional.

Attorneys representing couples who want to wed are preparing to rest their case Friday in the federal court challenge to California’s Proposition 8, turning over the courtroom to supporters of the gay-marriage ban.

The trial—the first to bring a state gay-marriage ban into federal court—will decide whether Proposition 8, a 2008 voter initiative that limits marriage to a man and a woman, violated the U.S. Constitution because it codifies discrimination.

Defenders of the law contend that it protects a legitimate state interest in encouraging opposite-sex couples to marry and have children in stable relationships.

Building their argument that Proposition 8 was motivated by discrimination, the plaintiffs on Thursday called to the stand a hostile witness who had asked to be dismissed as a defendant in the case because he feared for his safety.

Read the rest of Geoffrey Fowler’s Wall Street Journal article here.