More than 1,000 members of Heathrow Airport's security staff are set to strike for eight days in May.
Unite said the staff will walk out from May 4-6, 9-10 and 25-27 in a dispute over pay.
In total 1,400 staff members will walk out which is the same number who took 10 days of industrial action over Easter.
Unite general secretary Sharon Graham said: “Yet again, we have a chief executive who thinks it is acceptable to boost his earnings while he denies his own workers a decent pay rise.
“This dispute is bound to escalate with more workers being balloted and disruption set to continue throughout the summer.”
Unite regional officer Wayne King said: “Strikes next month will cause further disruption to airport passengers but this dispute is a direct result of Heathrow’s stubborn refusal to make an offer that meets our members’ expectations.
“Our members have been crystal clear they are seeking a substantial permanent increase in pay.
“A small one-off lump sum payment will not alleviate the financial pressures our members are facing on a daily basis.”
What did Heathrow Airport say in response to this?
A Heathrow spokesperson said: “We kept Heathrow running smoothly during the first 10 days of Unite’s failed industrial action, and passengers can have confidence that we will do so again this time.
“We will not let Unite disrupt the flow of visitors to the UK during such an important period for the country.
“Instead of chasing headlines, Unite should listen to its members.
“The majority of Heathrow colleagues do not want to strike and want to accept the offer on the table.
“Each day that Unite refuses to allow members to vote on the 10% pay increase and a £1,150 lump sum payment is a day that costs colleagues money they deserve now.”
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