ADELAIDE bus passengers will ride for free from next week after drivers voted for industrial action in support of claims for higher wages and better working conditions.

Transport Workers Union members voted "resoundingly'' in favour of specific action, which can include refusing to collect fares, overtime bans and rolling 24-hour strikes.

The union's first action involves its members refusing to collect fares indefinitely from Tuesday next week as it seeks public support and to put financial pressure on two of Adelaide's three bus companies, which carry the majority of passengers.

SA Branch secretary Ray Wyatt has not ruled out future strikes.

But he said "in recognition'' of outstanding public support drivers will not strike over the Australia Day Long weekend.

"We would like to thank the travelling public of SA and as of Tuesday there will be non-collection of fares or validating of tickets indefinitely,'' he said.

This action will be taken on the services provided by bus companies South Link and Transfield Services, which account for about two thirds of the network.

Mr Wyatt expects up to 15,000 passengers a day will travel free as a result of the planned action at a daily cost of around $100,000 in unpaid fares.

Union members, representing about two thirds of drivers, are concerned about a recent spate of violence against them, fatigue caused by work rosters and a lower wage rise offer than sought. Drivers wanted a 5 per cent pay increase but had been offered just 2.8 per cent by South Link and Transfield Services.

Transport Services Minister Chloe Fox said the State Government is not directly involved in negotiations "due to the privatisation of the bus contracts by the previous Liberal Government''.

"However, the Government has been talking regularly with the TWU and the two companies to ensure negotiations continue in good faith,'' she said.

The TWU sent about 600 members a ballot paper just before Christmas, seeking endorsement for industrial action.

The paper asked members to recommend specific industrial action, including refusing to collect fares, overtime bans and rolling 24-hour strikes.

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Voting closed this afternoon and the union must give three days' notice to Adelaide's three bus companies before taking action.

At least 50 per cent of drivers must vote in favour for industrial action to go ahead.

A TWU survey last year showed 27 per cent of bus drivers had witnessed a passenger being assaulted and more than one in 10 drivers said they'd been bashed on the job.

The union said work rosters causing driver fatigue were a safety issue for its members and other road users.

TWU senior SA organiser Ian Gonsalves said no public transport bus company was in breach of fatigue laws over rosters but they were in need of change.

"Some companies do a maximum four hours and 50 minutes driving in the first portion of their shift, have up to 70 minutes break and then do another four hours and fifty minutes driving,'' he said.

Originally published as Free bus rides due to wage dispute