JEFFERSON CITY – Missouri Gov. Jay Nixon said Thursday he is directing state tax officials to accept tax returns jointly filed by same-sex couples who have legally married in other states.

The Democratic governor said the executive order applies solely to tax filing status and does not authorize or sanction same-sex marriage in Missouri, which has a constitutional provision stating marriages must be between a man and a woman to be valid and recognized.

Missouri's tax code is tied to that of the federal government, and Nixon said married couples who file joint federal tax returns also must file state taxes jointly. The U.S. Treasury Department and Internal Revenue Service this year said legally married same-sex couples would be treated as married regardless of where they live. The decision came after the U.S. Supreme Court invalidated part of the Defense of Marriage Act.

Nixon said accepting jointly filed state returns for couples who file joint federal returns is appropriate.

"This is not about the definition of marriage," he said. "This is about the structure of our tax code."

Missouri in 2004 became the first state to enact a constitutional amendment prohibiting same-sex marriage after the Massachusetts high court permitted gay marriage there. The measure was approved by 70 percent of the vote.

Missouri House Speaker Tim Jones said Thursday that Nixon is trying to play all sides of the issue by "indulging his liberal ideals" while hedging his bet by stating the courts had "forced his hand."

"This executive order is nothing but an attempt to violate the voters' will, unlawfully ignoring a constitutional amendment to provide the governor's liberal allies a policy victory," said Jones, R-Eureka.

Speaking at a news conference at the state Capitol, Nixon said recognition of same-sex marriage is a separate question from the tax filing issue. However, he said he hopes voters will have a chance to revisit that. Nixon won re-election last year and is barred by term limits from seeking a third term as governor.

"I just don't think we should treat folks differently in this zone anymore," he said. "I think if folks want to get married, they should be able to get married."