Commuters in Melbourne and Victoria risk being left stranded again amid an ongoing pay dispute between the bus drivers' union and a state government contractor.
About 600 drivers staged a 24-hour strike on Tuesday, shutting down more than 70 CDC Victoria routes in Melbourne's east and west as well as in Ballarat and Geelong.
Services are set to return to normal first thing on Wednesday but the Transport Workers Union is planning a four-hour strike involving the same routes on Friday.
They also expect action next week after Victorian children return from their school holidays.
CDC has applied to the Fair Work Commission for mediation after the union rejected a 2.5 per cent pay rise offer and demanded four per cent.
TWU national vice president John Berger indicated strike action may extend to another bus operator, Transdev, in coming weeks.
"We have not taken strike action in the bus industry for 20 years," he said.
"This (pay) claim is not limited to CDC, it's across the bus sector and there are another 600-odd drivers with Transdev who might also take action."
CDC Victoria chief executive Nicholas Yap said Tuesday had been a "difficult day" and apologised to customers.
He added the company's pay offer included "industry-leading benefits".