Adelaide bus passengers will get a free ride from Tuesday after drivers voted for industrial action as part of their pay and safety dispute.
Transport Workers Union state secretary Ray Wyatt said between 10,000 and 15,000 passengers travel on the buses, meaning the move could cost up to $100,000 a day.
Drivers have "resoundingly" voted to take action and from Tuesday will not collect fares or validate tickets on buses driven by union members, he said.
About two-thirds of drivers are in the union and the action will take place indefinitely on public transport services provided by South Link and Transfield Services, which account for about two thirds of the network.
The union wants a five per cent pay increase while the companies have offered 2.8 per cent.
They also want improved safety measures for drivers, such as on-board security staff, and changes to broken shifts.
A union survey found that 15 per cent of drivers had been assaulted over a 12-month period, Mr Wyatt said.
SA Industrial Relations Minister John Rau said the dispute was not an issue for the government to become involved in, as it was between drivers and the two companies.