A massive bus strike that would thwart tens of thousands of commuters is set to go ahead on Friday, causing headaches for the Andrews government just over a month before the state election.

Over 900 buses at the state's largest bus operator, Ventura Bus Lines, could be stopped for 24 hours on Friday, as roughly 1000 drivers threaten to walk off the job in a fight for better pay.

The company runs SmartBus routes, and services schools, universities and medical centres.

The strike threat follows a breakdown in negotiations between the company and the Transport Workers Union, which is pushing for a 15 per cent wage rise over three years. The Age understands Ventura has not offered any increase.

The union is demanding a 4 per cent wage rise plus one per cent superannuation, per year, at every bus company in the state.