European flights during the summer holiday period could be affected by strike action by air traffic managers.
Eurocontrol, which manages flights over Europe, has said one of its unions could take industrial action, although no dates have been announced yet.
Negotiations are continuing with the union and other unions, Eurocontrol said.
Industry group Airlines UK urged Eurocontrol “to reach agreement as soon as possible”.
Another industry body, Airlines for Europe, said the possible impact of any strike action “remains to be determined”.
Eurocontrol said it was “making every effort to keep negotiations open and to find a constructive way forward”.
One of its trade unions, Union Syndicale Bruxelles, has “announced a period of six months during which industrial action could take place”.
It said the action could affect its Network Manager Operations Centre, which handles more than 10 million flights a year.
Prior to the pandemic, it had daily peaks managing more than 37,000 flights, and Eurocontrol said the centre played a pivotal role in managing, streamlining and improving air traffic.
Eurocontrol stressed that it was in “ongoing dialogue” with the union.
“As no notice of specific industrial action has been received, it is premature to speculate on any potential impact,” it said.
Airlines for Europe said any strike action would not affect Eurocontrol’s air traffic control services and “therefore its impact on passengers could be limited”.
The BBC has approached Union Syndicale Bruxelles for comment.
Aviation in Europe is facing a particular set of challenges this summer.
Demand for flights is returning to pre-Covid pandemic levels, and European airspace is being constricted by Russia’s war in Ukraine.
But there is a shortage of air traffic controllers, and some strikes are already planned – for example, there is an air traffic strike in Italy on Saturday 15 July.
Airlines UK said its members were “looking forward to a busy summer, meeting growing demand for travel and carrying millions of people on holidays”.
It said airlines have “made huge efforts since the pandemic to build resilience into operations”.
An agreement between Eurocontrol and union members would “avoid any potential disruption for airlines and their customers”, it said.
It added that air traffic controllers were already having to work within “a more constrained European airspace” due to Russia’s Ukraine war.
Travel expert Simon Calder said the union involved did not have a reputation for militancy, and that instead this was a “cry for help” over staffing levels.
During the height of the Covid pandemic in 2020, many older air traffic controllers retired, and have yet to be replaced, he said.
He said he expected this potential dispute to be resolved before it reached the stage of a strike.
But a more pressing concern was a lack of air traffic controllers in general, with impacts already being felt through “a series of cancellations every day in the UK”.
This comes as demand for air travel rebounds after the pandemic, he added, with Friday being the busiest day for air travel since 2019.
Last summer, holidaymakers were affected by sustained disruption to flights due to staff shortages, and across 2022 as a whole more than a third of UK flights were delayed.
Having axed thousands of jobs during the worst of the Covid pandemic, many aviation businesses including airports could not get new staff in place quickly enough.
But at Easter this year, airports and airlines told the BBC they were confident they had enough staff to avoid any travel chaos.
This summer, having raised staffing levels, disruption instead could come from industrial action.
Travel to France from the UK has already been affected this year by some strikes.
Source : BBC