Airports that will be directly affected are Dundee, Inverness, Wick, Kirkwall, Sumburgh, Stornoway, and Benbecula.
Action short of a strike will start on 1 April and continue throughout the summer to 31 August. This will include instruction to work to rosters; refusal of non-medical extensions; an overtime ban and withdrawal of good will.
Prospect will also seek to agree a protocol with HIAL to ensure cover for emergency incidents during the period of the strike.
David Avery, Prospect negotiations officer, said: “Prospect members have agreed to delay any strike action until after the Scottish school holidays. Our members do not want to stop their friends and neighbours visiting their families during the school holidays.
“I urge HIAL and Scottish Ministers to use the additional time members have given them to bring forward real proposals to resolve the dispute rather than the same offer which has already been rejected twice.”