The Australian Federal Police (ADP) said fraud allegations pertaining to alleged misuse of taxi dockets were being investigated since last month against Slipper.
"Police have now assessed that the matter requires further investigations," Sydney Herald Sun quoting a police spokeswoman as saying.
Slipper, who quit the Liberal Party last year when he became speaker, had to stand aside from his post last week pending possible criminal investigation into allegations that he had misused travel vouchers.
He also faces a criminal lawsuit brought by his adviser James Ashby involving allegations of sexual harassment between January and March this year.
The events around Slipper have come as a blow to Prime Minister Julia Gillard whose hold on power is fragile.
After initially backing the speaker, Gillard later distanced herself from him, as opinion polls showed the ruling Labor party facing rough weather in next year's general elections.
Meanwhile, another ruling party lawmaker Craig Thomson has is also under a cloud over allegations of misuse of credit card of his former employer, The Health Services Union (HSU) to pay for lavish meals, prostitutes and to get cash advances.
Police today raided the offices of HSU in the city seizing documents and computers.
In the face of the fresh scandal, Gillard has expelled Thomson from the ruling party, making her majority in Parliament razor thin. PTI HKR AKD