The political storm surrounding Toronto's ballooning employee sick day bank continued to grow Thursday as the city's audit committee probed why the program's true cost of $450 million wasn't disclosed earlier.

The probe comes amid allegations that Mayor David Miller low-balled the amount during the city's summer strike, when the sick day benefit became the strike's major issue.

The $200-million discrepancy is being blamed on a computer glitch at the actuary firm hired by the city. During the summer strike, the benefit's cost was said to be $250 million.

However, the city was supposed to report the true cost of the program to the auditor on June 22, which was also the first day of the strike.

And according to CTV Toronto's Janice Golding, the real cost of the sick days were known to city staff in March -- three months before workers walked off the job.

"Who knew what, and at what time?" asked Coun. Gloria Lindsay Luby on Thursday.

Still, Miller has stridently defended himself against any charges of a cover-up.

This week, Miller said he was made aware of the accounting error during the strike, but stressed he only spoke about the relevant costs of the sick benefits -- namely, those relating to the striking workers from the Canadian Union of Public Employees.

Since police and firefighters weren't on strike, the cost for their sick days wasn't included in the tab, Miller said.

"The figure that was used during the strike was $140 million. That is the amount owing for the CUPE sick bank liability. Figures related to police and firefighters were not relevant to the strike and were not used at the time."

Still, critics are asking that the mayor clamp down on the benefit as police and firefighters begin to negotiate new agreements with the city.