From Monday, unvaccinated passengers arriving in Portugal from Britain must quarantine for 14 days.
That's according to a Portuguese government statement issued late on Sunday.
The new rule, which will remain in place until at least July 11, comes amid a surge in cases in Portugal, where the number of daily new COVID-19 infections is back to February levels, when the country of just over 10 million was still under a strict lockdown.
Daily positive cases have also been rising in Britain for a month. Britons arriving in Portugal by air, land or sea must show proof they are fully vaccinated or self isolate for 14 days at "home or at a place indicated by health authorities."
Britain, one Portugal's biggest sources of foreign tourists, removed the southern European destination from its quarantine-free travel list earlier this month.
Portugal is on Britain's amber list, meaning holidaymakers must self-isolate for 10 days when they return home and take expensive COVID-19 tests.
Portuguese health authorities have blamed the more contagious Delta variant, first identified in India but rapidly spreading in Britain too, for the recent rise in infections.


Zohran Mamdani wins NYC mayoral race, capping meteoric rise
Death toll rises to 11 in fire at Bosnian retirement home
Driver rams into pedestrians in western France, nine injured
Philippines begins cleanup after Typhoon Kalmaegi leaves at least 85 dead
China's Shenzhou-20 return mission delayed due to space debris impact
