Irish airline Ryanair is launching legal action against Britain.
It's over the country's "traffic light" system for international travel.
The airline has teamed up with Manchester Airports Group, and the pair plan to file papers at England's High Court on Thursday (June 17).
They're seeking clarity over the transparency of the system.
With other airlines expected to join the move.
There are just weeks before the peak summer travel season when most airline profits are made.
The industry has repeatedly criticised the UK's traffic light system for international destinations.
Airlines say it is unpredictable and doesn't make scientific sense.
And that some low risk countries and islands should be open for travel.
A government spokesperson said it could not comment on legal proceedings.
Britain allowed vacations again from May after months of lockdown, but discourages travel to popular holiday destinations such as Spain, France, Greece and the United States.
They're classified as "amber" on the system, meaning travelers have to take multiple tests and quarantine for 10 days on their return.
Only a few places a listed as "green", and none in the EU.
The aviation industry had been banking on Britons to be at the forefront of the resumption in travel.
As the country has one of the fastest vaccine rollouts in the world.