Security staff will strike for another eight days next month in a dispute over pay, Unite union has announced.
Members of the union will walk out on May 4, 5, 6, 9, 10, 25, 26 and 27.
Unite said the strikes will cause “inevitable disruption and delays” at a time when people are expected to be travelling to the UK for the King’s coronation.
The 1,400 security officers involved in the dispute took 10 days of 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.”
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.”
Heathrow said it has been engaged in talks with Unite for months.
Its offer since January has been a 10% pay increase, but in talks last week it said it had improved the offer with a further £1,150 lump sum this year.
The airport said Unite was refusing to put the revised offer to its members.
The dispute involves security guards based at Terminal 5.
Other Unite members have voted against strikes, the airport pointed out.
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