A lawsuit is challenging Missouri Gov. Jay Nixon’s order that the state accept jointly filed tax returns from same-sex couples legally married in other states.

Nixon said the directive applies to tax filing status and doesn’t authorize same-sex marriage. The Missouri Constitution states only marriages between a man and a woman are valid in the state.

The lawsuit asks Nixon’s order be declared unconstitutional. It was filed by officials from the Missouri Baptist Convention Christian Life Commission and the Missouri Family Policy Council.

Missouri’s tax code is tied to the federal code. Nixon said couples who file joint federal returns must file state taxes jointly. Federal officials determined legally married same-sex couples would be treated as married regardless of where they live.

A Nixon spokesman declined comment about the lawsuit.