Security guards at Heathrow Airport are set to announce a fresh series of strikes in a pay dispute.
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.
Some 2,000 security guards across Terminals 3 and 5 are set to be covered by the strike action.
Unite General Secretary Sharon Graham said: “Escalating strike action will inevitably cause disruption, delays and cancellations across Heathrow.”
A number of airlines face disruption, delays and cancellation as a result of the expected Terminal Three walkout, including Virgin, Emirates, Qatar, United, American and Delta.
Walkouts at Terminal Five could also heavily affect British Airway’s summer schedule.
It follows three days of strike action held last week, with members of the union locked in a dispute with Heathrow Airport Limited (HAL) over pay.
Heathrow Airport has said that it continued to deliver good service during previous strikes, with most passengers waiting less than 5 minutes, and almost all waiting less than 10 minutes for security.
Speaking previously, Heathrow CEO John Holland-Kaye called the strikes “completely unnecessary”.
“When I speak to colleagues the overwhelming message is that they just want to vote on our pay offer, but Unite won’t let them,” he said.
“We made a generous 10% offer early on, to make sure colleagues got a substantial increase when they needed it most. Unite’s delays mean non-union colleagues as well as the majority of colleagues who are union members, who voted to accept our previous offer are losing out.”
