Fresh strikes by security guards at Heathrow airport are expected to be announced next week.
Members of Unite are embroiled in a long-running dispute over pay which has led to previous industrial action.
It is understood the new strikes were going to be announced on Friday, but it is now thought that notice will be served on the company next week.
In a statement Unite said: “The Unite notice regarding the industrial action at Heathrow is not live.
“It should be held at the moment until notice is served on the employer, next week.”
A Heathrow spokesperson said: “Passengers can rest assured that we will do everything we can to minimise strike disruption so they can enjoy their hard-earned summer holidays.
“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.
“The simple fact remains that the majority of colleagues do not support Unite’s strikes.
“There is a two-year inflation-beating pay rise ready for colleagues, if only Unite would allow them to have a say.
“We will continue talks with Unite about resolving this issue.”
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.