Unite has warned of “major disruption” at Heathrow as nearly 800 members of the union will take part in a week of strike action next month.
The walkout is set to start at 00:01 on May 7 and end at 23:59 on May 13.
The union said the action is planned after “management announced its intention to outsource hundreds of roles in a cost-cutting exercise”.
However, the airport said in a statement that it has “robust contingency plans” and anticipates “no impact on passenger journey”.
A Heathrow spokesperson said: “We are reorganising our operations to deliver better results for our customers. There are no job losses as a result of these changes, and we continue to discuss with Unite the implementation of these changes for the small number of colleagues impacted.
“Unite’s threats of potential industrial action are unnecessary, and customers can be reassured that we will keep the airport operating smoothly just like we have in the past.”
News of the action comes a day after a 72-hour strike at the airport by 50 refuelling staff on May 4-6 was announced.
Unite said the latest announcement is about the outsourcing of roles in passenger services, trolley operations and campus security by June 1.
The union said the three outsourced areas are being joined in industrial action by firefighters and airside operations from HAL “who recognise the deleterious impact outsourcing would have, fear that the fire service and airside operations may be next in line and support the idea of a multilateral collective bargaining agreement”.
Sharon Graham, Unite general secretary Sharon Graham said: “Heathrow Airport’s actions are deplorable; it is raking in massive profits for the bosses while trying to squeeze every last penny out of its workforce.
“Unite is fully focussed on defending its members jobs, pay and conditions and our members at Heathrow will receive the union’s unrelenting support during this dispute.”
Unite regional co-ordinating officer Wayne King added: “Strike action will inevitably cause widespread disruption across the airport, leading to delays and disruption.”