Security staff at Heathrow Airport have announced an escalation of strike action, with walkouts to take place nearly every weekend from mid-June to the end of August.
Members of Unite are embroiled in a long-running dispute over pay which led to industrial action last month and Easter.
From 24 June, 31 days of strikes will take place by more than 2,000 security staff. Officers from Heathrow Terminal 3 are joining the industrial action for the first time in the coming dates.
The workers will strike on:
• June 24, 25, 28, 29 and 30
• July 14-16, 21-24, and 28-31
• 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.
Heathrow said similar strikes in recent weeks by campus security and staff in terminal five had not been disruptive.
An airport spokesperson said: "Unite has already tried and failed to disrupt the airport with unnecessary strikes on some of our busiest days and we continue to build our plans to protect journeys during any future action.
"Passengers can rest assured that we will do everything we can to minimise strike disruption so they can enjoy their hard-earned summer holidays."
During the periods of industrial action - by roughly 1,400 security staff - passengers were only able to bring two carry-on items through security.
The union said the dispute could escalate further in the coming weeks.
It said Heathrow security officers are paid less than others at major airports in London and the South East. The officers, Unite said, were the highest paid before the COVID-19 pandemic but are now paid between £5,000 and £6,000 less a year than counterparts at Stansted and Gatwick airports.
Heathrow has said this is untrue and that Unite is not using like-for-like comparisons with airports that require anti-social working hours and to be on shift seven days a week.
The airport also said it was one of the only organisations during the pandemic not to make any frontline redundancies and a very small number of contracts were "aligned with current market rates".
But Unite's general secretary said Heathrow has "its priorities all wrong".
"This is an incredibly wealthy company, which this summer is anticipating bumper profits and an executive pay bonanza," Sharon Graham said.
"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."