Major Scottish airports have warned passengers may be impacted by problems with e-gates at passport controls.
The barriers are not working at airports across the UK causing delays for passengers.
Edinburgh Airport said it was working on contingencies with Border Force while it addressed the problem.
Meanwhile Glasgow International Airport said it did not have any significant queues so far, but entry to the UK may take longer than usual at peak times.
A spokesperson said that Border Force has additional staff in place to keep disruption to a minimum.
The issue affects all UK airports that use the gates, including Heathrow, Manchester and Gatwick. It began on Friday night.
It means people flying in are having to get their passports checked by Border Force staff manually.
The Home Office said it was working to minimise disruption from the “nationwide border system issue.”
The Immigration Services Union warned that queues would build quickly.
It is not known what the problem is with the border system, with a Home Office spokesman saying it was “too sensitive to say”.
The e-gate system speeds up passport control by allowing some passengers to scan their own passports. It uses facial recognition to verify identity and captures the traveller’s image.
E-gates can be used by British citizens aged over 12 and those from the EU, as well as people from countries including Australia, Canada, the US, Japan and New Zealand.
But all entry points retain manned security desks for other passengers and those unable to use e-gates.
A Home Office spokesperson said they were aware of a “nationwide border system issue affecting arrivals into the UK”.
“We are working to resolve the issue as soon as possible and are liaising with port operators and airlines to minimise disruption for travellers,” they said.