Mississippi Governor Phil Bryant, a Republican, has come out in support of a state law banning adoption by gay and lesbian couples.

Mississippi is the only state left with an outright adoption ban based solely on sexual orientation.

On Wednesday, four lesbian couples filed a federal lawsuit challenging the constitutionality of Mississippi's ban.

(Related: Four lesbian couples challenge Mississippi's adoption ban.)

“I hope the attorney general will vigorously defend the State of Mississippi against this lawsuit,” Bryant said in a written statement.

The Human Rights Campaign (HRC), the nation's largest LGBT rights advocate, criticized Bryant's stance.

“Gov. Bryant’s support of a state law that enshrines discrimination is shameful, especially coming at a time when it is imperative that we find permanent families and safe, loving homes for every child - including many in Mississippi currently in foster care,” said HRC Mississippi State Director Rob Hill. “We call on Attorney General Jim Hood to come down on the right side of history – don’t defend the ban, allow it to become another discarded artifact of discrimination.”

“With one-third of Mississippi's 3,484 same-sex couples already raising children and 100 Mississippi youth in foster care waiting for loving adoptive homes, shame on the governor for trying to keep Mississippi tethered to a discriminatory past,” he added.