Shadow Attorney-General George Brandis says the Prime Minister must rule out any link between Craig Thomson's arrest and her early calling of the federal election.
relating to allegations he misused Health Services Union money when he was its national secretary.
Senator Brandis told Lateline that Prime Minister Julia Gillard must explain whether the reason she called the election so far ahead of time was because she knew of Mr Thomson's impending arrest.
"It is a curious fact that this very, very surprising - indeed, historically unprecedented - announcement of an election seven-and-a-half months into the distance, took place literally 24 hours before Mr Thomson was arrested and charged," he said.
"Now, I'm not saying that there was a cause-and-effect relationship between those two things, but it is curious.
"The Prime Minister needs to make it clear that there was no such cause-and-effect relationship."
Ms Gillard took the nation by surprise on Wednesday when she announced the federal election would take place on September 14.
Just a day later, NSW police executed an arrest warrant at the request of Victorian police as part of their investigation into the Health Services Union (HSU).
Mr Thomson, the federal member for Dobell, appeared in Wyong Local Court yesterday afternoon where he was granted bail to appear in the Melbourne Magistrates Court next week.
One of the conditions of bail is he must not contact any person he is alleged to have engaged for sexual services.
He said he would "vigorously defend" the charges against him.
"As I have said from the start, I have done no wrongdoing and that's what will be found in these matters," he said.
The Opposition is continuing to use the Thomson scandal to question the Ms Gillard's political judgement.
Senator Brandis told Lateline that Opposition Leader Tony Abbott did not go too far in saying that Ms Gillard had run a "protection racket" for Mr Thomson.
"The fact is that the Prime Minister, exhibiting her characteristically poor judgment - the same poor judgment we saw when she picked Peter Slipper to be the Speaker of the House of Representatives - was for months, and indeed years, Craig Thomson's principal political defender and protector," he said.
Meanwhile, the civil case against Mr Thomson is due to begin in the Federal Court today.
The case is in regards to Fair Work Australia's allegations that Mr Thomson used union money to pay for prostitutes and support his election campaign.
Mr Thomson is not expected to be in court and his lawyers believe his arrest over fraud allegations yesterday will see the civil case postponed.