Portugal has questioned the UK's decision to add the country to its amber travel list, forcing visitors returning from the southern European nation to Britain to quarantine amid concerns over rising coronavirus cases.
Under the new rule change, people returning to the UK from Portugal will be required to quarantine at home for 10 days as part of COVID-19 restrictions.
The decision was announced by the British government on Thursday and comes amid a review of the UK's traffic light system for travel.
Those coming from red or amber countries have to quarantine on arrival in the UK, while those listed as green are exempt.
Portugal had been the only EU country in the UK's list of green countries but that will change from Tuesday, June 8.
"The decision to move Portugal (including Madeira and the Azores) to the amber list follows increased concern in the spread of variants of coronavirus, including a mutation of the Delta variant, and the risk that is posed of bringing these back to the UK if people are not required to quarantine," said the UK's transport ministry in a statement.
Shortly after the news was announced, a Portuguese ministerial social media account took aim at the shift, asserting that it "cannot understand" the UK's "logic".
The tweet came from the cabinet of Portugal's Minister of State for Foreign Affairs, with the account tweeting in English: "We take note of the British decision to remove Portugal from the travel 'green list', the logic of which we cannot understand."
"Portugal continues to carry out its prudent and gradual deconfinement plan, with clear rules for the safety of those who live here and those who visit us," it said.
The tourism industry has also voiced its opposition, anticipating the government's move in a statement earlier on Thursday.
“If Portugal has been dropped into the amber list, it will crush the confidence to travel, depress forward bookings and deter holidaymakers," said Virginia Messina, senior vice president at the World Travel and Tourism Council (WTTC).
"This will cause further stress to travel and tourism businesses already reeling from the green list announced just a few weeks ago.
“WTTC believes the time is now right for the UK to open the doors to safe travel and allow all those who are fully vaccinated or can show proof of a negative COVID-19 test, to travel freely.
“The UK could and should leverage its hard-won competitive advantage from one of the world’s best vaccine rollout programmes, to restore mobility and reopen the doors to safe international travel.”