Two further strike dates have been announced at Glasgow Airport which will take the industrial action into the summer holiday period.
Unite the union says workers including airport security officers, airport fire safety, airfield operations officers and engineering technicians will now strike on five days this month.
The industrial action will take place between 9.30am and 1.30pm on June 28, and between 5pm and 9pm on June 30.
It follows three previously announced dates for Glasgow, and two strikes planned for Aberdeen Airport.
Both are owned by AGS Airports, with the strikes coming in response to a breakdown in talks over pensions and pay.
Pat McIlvogue, Unite regional industrial officer, said: “The position of Glasgow Airport in this dispute has been to spend more on contingencies than it would cost to resolve this dispute which is economic madness.
“We continue to have real concerns over the competence and training levels of the workers brought in from England on a contingency basis by Glasgow Airport.
“We want the travelling public to be safe.
“So far, AGS have refused to withdraw the closure notice on the pension scheme, which breaks our Acas agreement with them.
“Unite wants the public to know that we want a remedy to this dispute and we remain ready to enter meaningful negotiations at any time, any place and under any auspices.
“But, this can only happen if AGS respond in kind with a willingness to put everything back on table.”
Other strikes at Glasgow are planned for June 21 (8.30am-2.30pm), June 24 (6am-10am) and June 26 (10am-2pm).
Industrial action at Aberdeen Airport is due to take place between 6am and 10am on June 27 and 28.
Mr McIlvogue added: “The industrial action will now roll into the summer holiday period with more days being added, and more to follow if AGS don’t get back round the negotiating table for meaningful discussions.
“Unite members have been left with no option but to defend their pension scheme and to fight for a fair pay increase.
“We hope the public understand that our members do not take this action lightly.”
Mark Johnston, managing director at Glasgow Airport, said: “This latest notice of industrial action is particularly disappointing given we have reached out to Unite and agreed a date for further talks which will take place at Acas next Wednesday 19 June.
“Despite their best efforts to cause disruption, we have kept our airport open ensuring thousands of passengers and hundreds of flights have been able to travel and operate safely. Our robust contingency plans will be in place on the new dates.”