Glasgow Airport workers to strike four times in two weeks
Unite members will now strike for a fourth day on June 21 over a pay and pension dispute.
Workers at Glasgow Airport will go on strike four times in the space of two weeks.
Members of Unite the union previously voted to take industrial action over a pay and pension dispute.
Following their strike on Friday, which saw passengers face delays getting through security, the union announced a further day of action.
In addition to the already announced 12-hour strike between 4am and 4pm on June 10 and four-hour protest between 4am and 8am on June 14, Glasgow staff will also take part in a six-hour stoppage on Friday, June 21 between 8.30am and 2.30pm.
Workers at Aberdeen Airport, who also took action on Friday, will again strike between 4am and 4pm on Monday.
Unite has blamed the industrial action "escalation" on AGS Airports Ltd - which owns both hubs.
The union claims that AGS has withdrawn from negotiations over its proposal to close its pension scheme to existing members.
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.
On Friday afternoon, Unite claimed that the strike had "severely disrupted" operations at Glasgow Airport.
Pat McIlvogue, Unite regional industrial officer, said: "The industrial action has severely disrupted Glasgow Airport's operations, despite the underhand tactics by management which included substituting fire safety officers with other staff on site who were questionably trained for the job.
"It's a shame that passengers' travel has been disrupted but this is 100% the fault of Glasgow Airport management."
"For the avoidance of doubt, Unite has repeatedly requested meetings with management and can categorically prove that we wanted to meet any time this week to try and find a resolution to this dispute.
"But, our overtures have been completely ignored which is why we have added further dates for industrial action. If we continue to be ignored then we will have no option but to escalate this dispute."
On Friday morning, Glasgow Airport apologised for the delays at security.
The airport tweeted: "We apologise to our customers for the delay at security this morning.
"Following the commencement of industrial action and transition to our contingency in security, we have experienced longer than normal queues."
A Glasgow Airport spokesman said: "We encountered longer than normal security times for a short period during our peak departure time this morning and would apologise to our passengers for any inconvenience caused.
"It is important to highlight that the airport is fully operational and our contingencies are in place.
"We are working hard to ensure we keep any disruption to an absolute minimum during this period of industrial action and our passengers remain our primary focus."
Aberdeen Airport said there were no delays or cancellations due to the strike.
Managing director Steve Szalay said: "This is not a situation that we want to be in but it's been business as usual here.
"We'll have 10,000 people travelling today and they've been coming in and out without disruption.
"These range from folk who've saved all year to go on holiday to people who have been working offshore and are getting home to see their families."