Ferry workers on the north boats have voted strongly in favour of striking.
The RMT union says workers on Serco’s Northern Isles services have voted nine to one in favour of industrial action.
The organisation has accused Serco of reneging on commitments, ripping up normal consultation procedures and announcing plans to press on with cuts to jobs and services.
In October Serco, which only recently took over the running of the North Isles service, announced it wanted to shed up to 36 jobs.
Following a ballot among RMT members, 95 out of 108 voted in favour of strike action. Only 13 were against, and there were no spoilt papers.
It was previously feared any strike action could happen over Christmas and New Year. The union’s national secretary, Steve Todd, said no decision had been made yet on exactly which dates the stoppages would take place.
He said members had been consulted over the move, and stressed workers were well aware of the possible impact any strike action could have on people in Shetland.
“We are still optimistic, even at this stage, of trying to find a resolution to the problem, which has been brought about by Serco.
“This overwhelming result shows that RMT members will not stand back while jobs are sacrificed in the middle of this botched privatisation stitch-up. Staff on Northern Isles routes are threatened with the sack in the dash to maximise Serco’s profits and that is totally unacceptable.
“The public will understand that it is our members’ jobs today and will be cuts to services and increases to fares tomorrow. Serco should withdraw this threat immediately and take up the offer of resuming talks through the proper consultation procedure as a way of resolving this dispute.”
General secretary, Bob Crow, said members had delivered a massive mandate for action.
“Serco are fully aware that we will not accept attacks on our members’ jobs and conditions and what is now an all-out attempt to bulldoze through redundancies, cuts to core staffing numbers and the casualisation of these skilled shipping grades.
“This ballot result, in the face of this deliberately provocative action, shows that our members are prepared to fight for their future livelihoods. The result will now be considered by the RMT executive.”
Meanwhile Isles MSP Tavish Scott has called on the Scottish government to step in and resolve the escalating fight between the union and employer.
Mr Scott said: “These boats provide Shetland’s lifeline shipping service. This is a government-funded contract which was renewed this summer. So the terms of the contract are the Scottish government’s responsibility.
“Ministers must stop dragging their feet and now get involved to stop industrial action which would be immensely damaging to local people and the islands’ economy.”