Australia's parliamentary speaker temporarily stepped down Sunday amid allegations of sexual harassment and fraud, touching off a political crisis that threatens Prime Minister Julia Gillard's tenuous grip on power.

House of Representatives Speaker Peter Slipper announced Sunday that he will be temporarily replaced by his deputy Anna Burke, a Labor Party government lawmaker, while police investigate allegations he misused taxi payment vouchers.

According in parliamentary regulations, the move effectively costs Gillard's government its single-seat majority.

While the center-left government will face greater difficulty in passing contentious legislation through the House of Representatives, the conservative opposition is still short of the 76 votes it needs in the 150-seat chamber to bring down the government.

Gillard, who has struggled to maintain her minority government since elections in 2010, welcomed the move.

"It is appropriate that Mr. Slipper has stood aside as Speaker whilst alleged criminal conduct is investigated," she said in a statement.

An openly gay male former staff member James Ashby, 33, made the fraud allegations and he is also suing Slipper in the Federal Court claiming sexual harassment. Slipper denies all the allegations.

Slipper, 62, who is married with two adult children from a previous relationship, defected from the opposition in November last year to take the speaker's job in a move that effectively gave Gillard's minority government an additional vote _ 76 in the chamber.

An independent lawmaker has since withdrawn his support for Labor, leaving Gillard with command of exactly half the chamber.

Since a speaker can only vote to break a draw, Burke will effectively be barred from most votes. The rules state that Slipper cannot vote at all while he stands aside.

But the absence of Slipper's vote creates the possibility of a 74-vote tie, in which the speaker's casting vote would come into play for the government.

The sexual harassment case is a civil matter, while the taxi voucher allegations are criminal. Police have confirmed they are evaluating the criminal allegation.

"Any allegation of criminal behavior is grave and should be dealt with in a manner that shows appropriate regard to the integrity of our democratic institutions and to precedent," Slipper said in a statement after returning from the United States on Sunday.

"As such, I believe it is appropriate for me to stand aside as speaker while this criminal allegation is resolved," he said.

"The allegation is incorrect, and once it is clear they are untrue, I shall return to the speakership. I would appreciate the relevant bodies dealing with the matter expeditiously," he added.

If Slipper had not stood aside, the opposition had threatened to move a motion calling for Parliament to dump him when it next sits on May 8.