Nixon said the directive applies to tax filing status and does not authorize same-sex marriage. The Missouri Constitution states only marriages between a man and a woman are valid in the state.
The lawsuit asks that Nixon’s order be declared unconstitutional and implementation of it blocked.
The suit was filed by the Missouri Baptist Convention Christian Life Commission and the Missouri Family Policy Council.
Missouri is one of 24 states coupled with the federal government for tax filing purposes, and Nixon said couples who file joint federal returns must file state taxes jointly.
Article continues belowFederal officials determined legally married same-sex couples would be treated as married regardless of where they live.
“Gov. Nixon’s pragmatic and reasonable order ensures that Missouri income tax law continues to mirror the Federal Treasury and IRS,” said A.J. Bockelman, Executive Director of PROMO, a statewide advocacy group.
“The plaintiffs have no grounds to file this case, the Governor’s order should stand,” said Bockelman.
A Nixon spokesman declined comment about the lawsuit.