The Scottish Government says it is "not satisfied" that a move towards testing travellers instead of telling them to quarantine would protect people from coronavirus.
As of 4am today, anyone arriving into Scotland from Portugal has to self-isolate.
It comes after a rise in cases in the country - and just two weeks after it was added to the safe travel list.
Yesterday, Boris Johnson said it was the UK Government's view that testing in airports may give a "false sense of confidence".
Despite that, the Scottish Conservatives believe it could be part of the solution - amid concerns about the impact the constantly changing rules are having on the travel industry.
The party's transport spokesperson is Graham Simpson MSP:
A spokesperson for the Scottish Government said: "We understand industry concerns and we do want to continue to explore whether there is a better balance around quarantine, but we are not satisfied that moving from quarantine to testing would provide enough protection - people in the early stages of incubation of the virus could test negative and go on to develop the virus and spread it.
"If we don't keep the virus under control, we make life even harder for the economy and particular sectors - as discussions continue we will hopefully find a balance that manages to weigh up both the public health and economic arguments.
"Regular discussions continue with the other three governments in the UK. We continue to closely monitor the situation in all parts of the world and base the decisions we make on the scientific evidence available.
"“We will continue to support the aviation industry and staff who have lost their jobs through our PACE initiative. As part of our business support package, which now exceeds £2.3 billion, we have provided business rates relief for aviation, airports and ground-handling providers - something that is not available in England or Wales.
"We are also urging the UK Government to extend the job retention scheme or to introduce alternative sector-specific support for those sectors that have a much longer recovery period."
Westminster has so far rejected calls to continue the furlough scheme beyond October, repeatedly pointing out that it has already provided support for tens of thousands of jobs and businesses in Scotland.
Earlier this week, quarantine rules were also introduced fro travel to Scotland from Greece.
Travel industry leaders have accused ministers of "playing games" and not giving consistent guidance to the public.
Michael Matheson MSP, the Scottish Government's cabinet secretary for transport, infrastructure and connectivity, is set to meet with representatives from Scotland's airports next week.
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