Ryanair and several British airports say they will sue the UK government over the implementation of international travel restrictions.
The Irish airline said on Thursday it would use legal action to obtain more transparency in health measures on international travel.
The lawsuit also includes the Manchester Airports Group (MAG), which also owns London Stansted and East Midlands terminals.
The companies say the UK government must explain how it makes its decisions on the so-called traffic-light system for foreign countries.
The UK currently lists countries as “green”, “amber”, and “red” based on health risks associated with the COVID-29 pandemic.
The airline industry has repeatedly criticised the government in recent weeks, claiming that travel to Europe’s sunny destinations is safe in the light of progress in vaccination and the decline in the number of cases.
The UK was widely condemned for reversing a decision on Portugal this month after only weeks, which forced people returning home to quarantine for 10 days, or cut short their trips.
Since Portugal’s withdrawal, no major European tourist country has been on the “green” list, which allows return to the UK without quarantine. Spain, Italy, France, and Greece are other countries on the “amber” list.
MAG has said other airlines should support the legal action against the UK’s health and transport ministries.
“Recent developments suggest that the government does not want to reopen international travel by placing low-risk countries on the green list,” said Charlie Cornish, MAG’s chief executive.
“Most countries seem to be stuck in the amber list for no obvious reason” despite lower levels of infection than in the UK, he added.
The airports and airliners say the lack of transparency has made it difficult for tourists to book their holidays, and for companies to prepare for the recovery.
Michael O’Leary, chief executive of Ryanair, said that “the UK’s traffic system has been a complete disaster from the start”.
“We call on Prime Minister Boris Johnson to explain the science behind the system … and to establish a transparent model based on the data that can restore confidence before the crucial summer months.”
The UK government has indicated it would review allowing vaccinated citizens to travel to the country amid the growing pressure.