Ryanair and the owner of Manchester, London Stansted and East Midlands airports are to launch a legal challenge against the government over the travel traffic light system.
They are calling for more transparency about how government decides which countries qualify for the green list of safe places to visit amid the pandemic.
It is understood that it has the backing of other major UK airlines.
Ministers say the system “cautiously manages the risk of new variants”.
The traffic light system rates countries green, amber or red based on their Covid-risk.
Travelers to countries rated green will not need to isolate on their return, but they will need to take a Covid test before and after their trip.
Arrivals from amber countries will need to quarantine, while red-list countries have the strictest rules, with only UK or Irish nationals, or UK residents, allowed to return – and they must pay for a 10-day in a government quarantine hotel.
The challenge by Ryanair and Manchester Airports Group has been put together after huge frustration within the travel industry at the inclusion of Portugal on the green list in mid-May and then its sudden removal a few weeks later.