The Australian Government Solicitor says the legal bill for the investigation into federal Labor MP Craig Thomson has cost taxpayers $912,562.
Mr Thomson denies he misused a work credit card to pay for prostitutes when he was employed as a Health Services Union official.
Fair Work Australia (FWA) is conducting an inquiry into the union's finances and the Government Solicitor says it is providing ongoing legal services.
The Federal Opposition specifically asked for the Solicitor's staff working on the case to attend today's Senate Estimates.
But the Solicitor's chief executive, Ian Govey, has told the estimates committee that FWA has instructed his office not to comment on details of the investigation.
"It would have been open to them to tell us that we could disclose further information, but I reiterate again that to do so would be inconsistent with normal practice," he said.
"Other questions about the services ADS has provided should be directed to FWA."
Opposition frontbencher Christopher Pyne used Question Time today to quiz Prime Minister Julia Gillard about the cost of the inquiry.
