Escalation in dispute over Hial air traffic plans
Prospect members at Highlands and Islands Airports Ltd (Hial) are to take further action in a dispute over centralising some air traffic control.
Hial has proposed controlling air traffic at five airports from a central hub.
The union Prospect said the move would result in the loss of 50 jobs.
Its members working in air traffic services are to "escalate" industrial action they started on 4 January this year.
The further action includes an overtime ban and refusing to work extensions to shifts except for search and rescue, emergency and medical flights.
The staff will also refuse to start some training of new controllers..
Prospect said Hial's modernisation plans would cost jobs and have an impact on island communities.
David Avery, Prospect negotiator, said: "This is the wrong plan and at a time when aviation is being decimated by the pandemic there are better things to spend taxpayers' money on."
Hial's plans would see a reduction in staff at its island airports in Lewis, Orkney and Shetland.
Air traffic service posts would also go at Dundee Airport.
Hial said it must modernise its air traffic control and its aim was to relocate current staff to the new hub in Inverness.