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 call for more transparency about how the government decides which countries qualify for the green list of safe places to visit amid the pandemic.
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.
Travellers 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 stay 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.
On top of this, the travel industry believes the Balearic and Greek Islands should have been included on the green list of countries last month when health data was analysed.
The boss of Ryanair, Michael O’Leary, wants Boris Johnson to explain the scientific basis behind the system which he says the government “seems to make up” as it goes along.
Further signatories to the challenge are set to be revealed on Thursday. They are demanding a fast response as the crucial summer season edges closer.
The government said at the time that moving Portugal from the green to amber list was necessary because of an increase in infection rates in the country, and the emergence of the “Nepal variant”, a mutation of the Delta version of the virus first detected in India. There were concerns that vaccines would not work as well on this particular mutation.
Travel bosses are concerned the damage of these sudden reversals will continue to erode the confidence of the British travelling public.
A government spokesperson said: “We recognise this is a challenging period for the sector, as we seek to balance the timely reopening of international travel while safeguarding public health and protecting the vaccine roll-out.”
“We have provided £7bn to help support for the industry during the pandemic.”
The spokesperson added that the government could not comment on legal proceedings.