A federal judge in San Francisco has refused to dismiss a lawsuit seeking to overturn California's same-sex marriage ban.

U.S. District Chief Judge Vaughn Walker also signaled Wednesday that the measure's sponsors will need to show that allowing gay couples to wed threatens traditional male-female unions.

Walker said significant questions remain about whether the voter-approved ban discriminates against gays and lesbians in violation of the U.S. Constitution.

Before ruling, Walker grilled a lawyer for the measure's backers who asserted that Proposition 8 was legitimate because it fostered "naturally procreative relationships."

The judge demanded to hear how that goal would be undermined if same-sex marriages were legal.