Portugal could be put back on the UK quarantine list due to a rise in coronavirus cases.
And an airline boss has warned that the move would cause 'chaos and hardship' for travellers.
Portugal was only removed from the UK’s quarantine list less than a fortnight ago meaning passengers arriving in the UK from the country didn't have to spend 14 days self-isolating.
However, British holidaymakers could end up facing the quarantine at short notice.
There were 21.1 coronavirus cases per 100,000 people in Portugal in the seven days to August 30, up from 19.4 in the seven days to August 29.
A seven-day rate of 20 is the threshold above which the UK Government considers triggering quarantine conditions.
Writing in The Times, Willie Walsh, chief executive of International Airlines Group, which is British Airways' parent company, said: "Another U-turn by the Government, adding Portugal to the quarantine list, will cause further chaos and hardship for travellers."
He said the "ever-shifting list" of countries requiring quarantine means "the UK has officially hung up the 'Closed' sign”.
Mr Walsh said: "The Government is using arbitrary statistics to effectively ban 160 countries and in the process destroying the economy.
"The Government needs to introduce a testing regime to restore confidence."
The warning comes after travellers returning from Switzerland, Jamaica and the Czech Republic were the latest to be told they must quarantine for 14 days if they were arriving in the UK after 4am on Saturday following spikes in coronavirus infection rates.
