Arlene and Paul Haslen were shocked to hear the instruction when they contacted the firm days before they were due to travel to ask why they had not received their test kits.
The ambulance technician and her paramedic husband had been repeatedly assured the kits would be sent after booking the holiday three weeks ago.
They were then told they would have to take their test kits to a Tui branch in England as none of those in Scotland would accept them.
The Haslens decided instead to travel to Edinburgh Airport to arrange their own tests – itself a 180-mile round trip – so they would have the results in time.
However, the couple’s holiday plans were scuppered when Portugal was moved from the green to amber travel list on Thursday – two days before they were due to fly from Glasgow to Faro for their two-week break.
They were then angered at being refused a refund for the £2,500 trip after the problems they had had over the tests.
The Scottish Ambulance Service staff said they would have had to return to work as soon as they returned, so would have been unable to self-isolate at home for ten days, as required after visiting an amber list country.
Mrs Haslen said: "That’s the disaster of our holiday.
"We’re absolutely devastated.
"The one thing we had to look forward to was this holiday and it’s just been pulled from under us.
"We’ve had nothing but hassle from Tui – they’ve been so unhelpful.
"They’ve got our money, so we’re stuck.
"We have to go with them next year whether we like it or not.
"They’ve got us by the short and curlies, because there’s nothing that we can do.
"If we could self-isolate when we come back, we would, but we can’t because of our jobs."
Tui, the world’s largest travel firm, said it had contacted the couple today to apologise but did not offer a refund for the holiday.
It said customers due to travel to Portugal up to June 17 were being offered free re-booking to other dates or destinations instead.
However, for those who wanted to cancel, “normal terms and conditions would apply".
A Tui spokesperson said: “We’re very sorry about Mr and Mrs Haslen’s experience with us.
"We’ve reassured them that their feedback is being taken seriously, and have apologised for the confusion over testing, which has been refunded in full.
"We want to offer our customers flexibility and choice this summer, so where borders are open and UK Foreign, Commonwealth & Development Office advice allows travel, we will operate to those destinations, including Portugal.
"We know some customers may be unsure about travelling this summer, so we’ve offered free changes 14 days before travel for anyone due to travel before the end of August.
"We constantly review our holiday programme and cancellations in line with the government updates every three weeks, with the next update expected on June 24."