Flights to and from Portugal will be disrupted today (Thursday) due to a general strike.
The 24-hour industrial action started at midnight and has led to some cancellations and warnings of delays.
Thomson Airways said the strike might impact its flying programme and warned passengers to be prepared for delays and pack any essential items such medicine, nappies and baby food in their hand baggage.
Monarch said passengers should check in early where possible.
"There is still some uncertainty about the impact of the strike but some disruption to flights in and out of Portugal is inevitable," it said.
British Airways said there are currently minor delays on the inbound and outbound service to Lisbon, but filghts to Faro are planned to operate as normal.
TAP Air Portugal said it plans to run all flights as scheduled but said there may be some operational disruptions. It asked passengers to arrive at the airport earlier than usual.
EasyJet and Ryanair have cancelled flights to and from Portugal, but none are from the UK.
EasyJet said the strike was likely to impact its flights through Faro, Funchal and Lisbon although flights to Oporto will operate as planned.
The airlines also warned that public transport in Portugal is also expected to be disrupted, so passengers should allow plenty of time to travel to the airport.
The general strike was called in response to austerity measures being imposed by the Portuguese government and record unemployment.
