MADISON, Wis. -- The Wisconsin Supreme Court heard arguments Tuesday that the state's ban on gay marriage should be set aside because lawmakers didn't follow the right procedure to amend the state constitution.

Attorney Lester Pines told justices on Tuesday that voters must be asked separately about every change proposed to the constitution, and that didn't happen during the 2006 vote.

In 2006 when voters got the controversial constitutional amendment banning gay marriage, they were asked one question with two parts, and passed it.

University of Wisconsin-Oshkosh political science professor William McConkey contends that the procedure was illegal because voters should have been able to vote on each part separately.

"The first section (of the amendment question) relates to the definition of marriage -- only a marriage between one man and one woman. The second section relates to something other than that," Pines, McConkey's attorney, told the court's justices.

The second section outlaws giving legal status like or similar to marriage to unmarried couples, essentially banning civil unions.

But Pines said the two issues are distinct and separate from one another and that lawmakers violated state law by holding only one vote on them.

The state attorney general denies that.

Assistant Attorney General Lewis Beilin said the constitution was correctly amended because the two parts of the amendment question were closely related.

Beilin also asserted that McConkey has no right to bring a challenge because he can't claim an injury.

The state said McConkey has no injury to claim, because even if the two pieces of the amendment had been separate, he would have voted the same way.

"McConkey conceded that even if the two propositions in this amendment were presented separately he would have voted no to each one," Beilin told the court.

The court is expected to rule by the summer. Even if the court overturns the constitutional ban on gay marriage, it will still be illegal under state law.