PHOENIX (AP) -- An Arizona state senator faces an ethics investigation for cutting off a debate that served as a filibuster for opponents of a referendum to prohibit same-sex marriage.

With its chairman crossing party lines, the Senate Ethics Committee voted 3-2 on Monday to formally investigate a lawmaker's complaint that Republican Sen. Jack Harper of Surprise broke Senate rules.

Harper was Senate debate chairman on June 27, the last day of this year's legislative session, when he halted delaying tactics by other senators who were trying to string out discussion of unrelated legislation in order to postpone or prevent a vote on the marriage referendum.

While presiding over the Senate, Harper abruptly transferred the right to speak from one of the senators participating in the filibuster to a supporter of the marriage measure.

The Senate narrowly approved the referendum later that day, sending it to the Nov. 4 ballot. If approved by voters, Proposition 102 would amend the Arizona Constitution to recognize marriage only as a union of one man and one woman.

Ethics Committee Chairman Jay Tibshraeny, R-Chandler, joined Democratic Sens. Marsha Arzberger of Willcox and Richard Miranda of Phoenix in voting for the investigation.

Holding a hearing to take testimony will allow the Senate to "clear the air" on the issue, Tibshraeny said.

The committee's other two Republicans, Sens. Robert Blendu of Litchfield Park and Barbara Leff of Paradise Valley, voted against the motion.

Sen. Ken Cheuvront, a Phoenix Democrat who was participating in the filibuster with the Senate's other acknowledged gay member, filed the complaint against Harper. It asks that the full Senate reprimand Harper.

Cheuvront said Monday that he welcomed the decision to investigate. It's important for the Senate to maintain its processes for fair and orderly debate, he said.

Harper left the hearing room once Tibshraeny cast the deciding vote, and he did not immediately return a call for comment.

However, he later issued a statement that, like his written response to the complaint, said the marriage measure opponents were not engaged in real debate and were not entitled to retain the floor.

Harper's comments during the June 27 floor session indicated his action to clear an electronic registry of senators wishing to speak was inadvertent, and Miranda said the apparent discrepancy between Harper's explanations for his actions merited investigation.

Blendu said he favored dismissing the complaint because there wasn't "demonstrable" evidence of misconduct.

Leff said not knowing how to properly preside over a Senate floor session should not be considered an ethics violation. She said there were misunderstandings about the rules throughout that day.

Arzberger said she was troubled that numerous shouted requests for immediate clarifications or explanations of procedural matters were ignored after Harper cut off debate. "That's an important part of our rules that was ignored," she said.

Tibshraeny said he anticipates the committee will meet next week to discuss how to conduct the investigation. He said any testimony would be sworn but that he didn't know whether the committee would compel testimony.

He said he anticipates hearing testimony from at least Harper and Cheuvront. He said he didn't know whether testimony would be sought from Senate Majority Leader Thayer Verschoor, R-Gilbert.

Verschoor, who has not responded to numerous requests by The Associated Press to comment on his role in the June 27 floor session, was the senator that Harper recognized to make a motion to end debate.

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