Air traffic controllers in Portugal will be on strike on 12, 13, 19, 20 and 26 April between 7am and 9am, Portugal time.
This will delay some flights, but airlines are trying to reschedule affected flights outside the strike time frames.
On 12 and 13 April, British Airways flight number BA499 from Lisbon to London Heathrow has been re-timed to depart at 0900hrs, 45 minutes later than scheduled. It is now due to arrive London Heathrow at 1140hrs.
The departures level in the terminal is expected to be heavily congested and passengers are advised to allow plenty of time and to check-in as normal.