A series of fresh strikes by security guards at Heathrow Airport in a dispute over pay has been announced.
The Unite union said more than 2,000 of its members will walk out for 31 days from June 24.
For the first time security officers based at Terminal 3 will join their colleagues from Terminal 5 and campus security who have already taken industrial action.
No Government intervention to ensure passengers are not delayed is currently planned, Downing Street said.
Unite general secretary Sharon Graham said: “Unite is putting Heathrow on notice that strike action at the airport will continue until it makes a fair pay offer to its workers.
“Make no mistake, our members will receive the union’s unflinching support in this dispute.
“Heathrow Airport has got its priorities all wrong.
“This is an incredibly wealthy company, which this summer is anticipating bumper profits and an executive pay bonanza.
“It’s also expected to pay out huge dividends to shareholders, yet its workers can barely make ends meet and are paid far less than workers at other airports.”
The workers will be on strike on June 24, 25, 28, 29 and 30, and July 14-16, 21-24, 28-31 and August 4-7, 11-14, 18-20 and 24-27.
The strikes will coincide with the beginning of the school holidays and the August bank holiday.
Military personnel were drafted in to check passports at UK airports including Heathrow during Border Force strikes in December.
Asked if the Government is planning anything similar for the forthcoming round of industrial action, a No 10 spokesman told reporters: “I’m not aware of it as things stand now, but, as I say, of course we will continue to keep an eye on the situation.
“We obviously recognise that this will be a major concern for those who are looking to travel over the next few months and those who are looking to get away on their summer holidays.
“Ultimately it’s a matter for Heathrow and the union to resolve, but we expect operators to make every effort to minimise disruption and to ensure those who are reliant on their services and those who have booked flights can still travel.”