Circuit Judge Jon Beetem will hear arguments Thursday afternoon on the request that he issue a restraining order in the same-sex tax returns case.
And Beetem on Friday approved the ACLU's request to intervene in the case on behalf of same-sex couples affected by it.
Last November, Gov. Jay Nixon issued an executive order telling the state Revenue department to accept "combined" tax returns from same-sex couples who were married in another state, and who file federal forms as a "married" couple.
The governor cited a state law that says: "A husband and wife who file a joint federal income tax return shall file a combined (Missouri) return. A husband and wife who do not file a joint federal income tax return shall not file a combined return."
And, he told reporters last November, the Internal Revenue Service changed its definitions of "marriage" for federal tax forms after the U.S. Supreme Court struck down a part of the federal "Defense of Marriage Act," for same-sex couples married in states - like Iowa - where those marriages are legal.
In January, four Missouri citizens filed a lawsuit asking the court to block Nixon's order, saying it violated the voter-approved constitutional amendment that says Missouri recognizes "only" a marriage between one man and one woman.
This week, Mike Whitehead, a Kansas City attorney representing the four plaintiffs in the lawsuit, asked Beetem to issue a temporary restraining order so that the Revenue department won't process tax forms it already has received, under terms of Nixon's order.
"Plaintiffs, as taxpayers, have already suffered, and will continue to suffer, immediate and irreparable harm if Defendants continue to promote and implement the challenged policy," Whitehead wrote in the motion.
"Once taxpayer funds are disbursed to administer this policy, and once combined returns have been accepted, it will be more expensive if not impossible for such expenditures to be recouped or for such actions to be undone."
Nixon's order last November also pointed to another state that says: "Any term used in (the law) shall have the same meaning as when used in a comparable context in the laws of the United States relating to federal income taxes, unless a different meaning is clearly required ..."
But opponents argue Nixon's first duty is to the Missouri Constitution and its rejection of those marriages - with some opponents noting the constitutional language clearly requires a "different meaning" from the one Nixon used.
During Friday morning's hearing, Whitehead told Beetem the state would represent the interests of the ACLU's clients, so the agency didn't need to be added as an intervenor.
But Solicitor General Jim Layton told Beetem the ACLU will argue that Missouri's marriage restrictions in the Constitution and state law violate the U.S. Constitution, while the attorney general's office doesn't support that argument.