The travel industry has reacted angrily to the decision to remove Portugal from the green travel list.
The popular holiday destination, which only reopened for Northern Irish tourists just weeks ago, was moved to the amber list and no new destinations were added to the travel green list
Reacting to the decision, a spokesperson for Belfast International Airport said the move was "incredibly disappointing for everyone affected."
"We understand and appreciate that safety comes first but this news is another devastating blow for our industry.
"As we continue to ease lockdown measures and the vaccination programme is progressing well we remain optimistic that summer holidays to Europe will be a reality.”
However, the change in the travel rules did not deter some travelers who flew out of Belfast on an EasyJet flight to Faro, just the morning after the change was announced.
"Gutted but we had everything booked. We had this holiday booked for two years, we've had to change everything," one traveler told UTV.
Another said that they would simply work from home on their return to Northern Ireland because of the new isolation rule.
A family told they had considered changing their flight to come back early, but decided against so they could spend more time with family in Portugal.
For travelers already in Portugal, returning home before Tuesday's change in rules is proving difficult.
Adrian Wells cannot afford to isolate as he is starting a new job when he returns from a trip travelling around Portugal.
The move to change the rules took him by surprise.
"I'd heard rumours but I didn't think it would happen as quickly as it did and everything's just moving a a hundred miles an hour'," Adrian told UTV from his hotel in Lagos, Portugal.
"I was meant to be going home next Wednesday so frantically yesterday afternoon, I had to book forward my flight to Sunday evening at a bit of cost for that.
"My main issue at the minute is my testing," Adrian explained, referring to the mandatory tests travelers must take before returning to Northern Ireland.
"I was due to do a test I had with me and I had organised that was in the parameters of the Northern Ireland government.
"I was about to do that and schedule the appointment in line with next Wednesday and then I've tried to pull that forward to get the testing done in time for the flight on Sunday but there's no more slots left," Adrian said.
"My day unfortunately ahead of me is to get a PCR test locally done and that's going to cause a lot of stress and expense.
"For me it's been handled quite badly. The timing is not great. I believe to find out late on a Thursday that you have to be essentially home on Monday is too soon.
"They should've given us more warning and a bit more time, taking into account the testing element. It's proving very very difficult," Adrian added.