Workers at Aberdeen Airport will go on strike four times in the space of a month.
Members of Unite the union previously voted to take industrial action over a pay and pension dispute.
Following strikes on Friday and Monday, which saw passengers face delays getting through security, the union announced two further days of action with four-hour stoppages between 6am and 10am on June 27 and 28.
Workers at Glasgow Airport, who also took action last Friday and Monday, are also set to strike again between 4am and 8am on Friday, between 8.30am and 2.30pm on June 21, between 6am and 10am on June 24, and between 10am and 2pm on June 26.
Unite has blamed the industrial action “escalation” on AGS Airports Ltd – which owns both hubs.
The union claimed that AGS made a repackaged 3% pay offer on Wednesday, but “restated their unwillingness to discuss or reopen the consultation on closing the pension scheme, which sets unacceptable preconditions for any further negotiations with Unite”.
Unite state that the decision has “broken an existing ACAS agreement made in 2016”.
Those involved in the strike action include security staff, fire and airfield support staff.
Shauna Wright, Unite regional industrial officer, said: “Unite members will now undertake two further days of industrial action at Aberdeen Airport following this latest pitiful attempt to divide and conquer by AGS.
“We want the public to understand that our members do not take this action lightly. But, AGS have repeatedly set preconditions to any negotiations by stating they will not reopen the consultation on the pension scheme, which breaks our ACAS agreement with them.
“Unite members remain strong and resolute, and they are determined to stand united with their fellow members in Glasgow who are facing the same attack on their pay and pension scheme by AGS.
“For the record, Unite wants to reaffirm that we are always open to meaningful negotiations to seek a remedy to this dispute at any time, any place and under any auspices. The ball is in AGS’ court.”
In response, Steve Szalay, managing director of Aberdeen International Airport, said: “It’s extremely disappointing that the trade unions have served notice of further strike action, particularly when we have agreed a date for talks and tabled an improved offer with a view to reaching a resolution.
“If they are serious about entering into meaningful dialogue then we would call on them to end the strike.
“Despite the best efforts of the unions to cause disruption for the travelling public, we have kept our airport open ensuring thousands of passengers and hundreds of flights have been able to travel and operate safely.
“We will once again put our contingency plans in place to ensure the unions do not cause disruption for passengers and airlines.”