The company that operates the bus that slammed into the notorious Montague Street bridge last year could be fined as much as $1.5 million after it was charged by Transport Safety Victoria.

A dozen people were injured when the Gold Bus operated by Bacchus Marsh Coaches hit the three-metre-high South Melbourne bridge on February 22. The bus was 3.8m high.

It took firefighters nearly an hour to free four people trapped inside the vehicle.

Four passengers suffered serious injuries, one with broken bones and another spent three days in intensive care. Twelve people in all, including the driver, were taken to hospital.