The threat of strike action by security staff at London Gatwick this weekend has deepened after their employer angered unions by threatening to sack anyone who takes part.
Unite the union said hopes of resolving the strike have receded, accusing bosses at ICTS (UK) of intimidation.
It said if the strike goes ahead it is likely to cause considerable delays and disruption at the airport.
As a result of the threats from ICTS, Unite has announced a further four days of strike action beginning on Tuesday August 20 ending on Saturday August 24.
"The behaviour of ICTS is deplorable, rather than seeking to resolve the dispute through negotiation they have instead decided to threaten and intimidate our members," said Unite regional officer Jamie Major.
"Rather than scare our members into submission this hamfisted attempt at intimidation has instead strengthened members’ resolve to secure a decent rate of pay."
More than 130 workers, employed to scan passengers’ luggage, are due to begin a 48-hour strike from 06:00 on Saturday (August 10).
Unite has refuted ICTS’ allegations that the strike is unlawful in any way, arguing that workers voted by 95% in favour.
Workers are asking for a 50p an hour increase in pay to £9 an hour.
"Our members undertake a crucial role which keeps passengers and airport workers safe, it is simply astonishing they are paid below the living wage for the work they do," said Major.
"If ICTS wishes to resolve the dispute, then the company needs to drop the threats, sit down at the negotiating table and end poverty pay rates for its members."
A spokesman for Gatwick Airport said: "We have been reassured by ICTS that the mitigation plans in place mean that flights will not be impacted at Gatwick. In the interests of our passengers, we continue to encourage both sides in this dispute to work towards a resolution."
