This comes as it is confirmed that a strike by British Airways cabin crew will go ahead after talks between the airline and the Unite union collapsed.
“There may be a knock-on effect after the strike and we have published details on our website of what passengers can do if their flight is cancelled,” a BA spokeswoman said.
The warning means that BA passengers could face disruption on a continuous basis from today until after the second, planned strike — from March 27 to 30 — is over.
BA is confident it will be able to handle as many as 49,000 passengers on each of the first two planned strike days, today and Sunday. This compares with a figure of around 75,000 for a normal weekend day in March, with some passengers due to travel with other carriers.
This weekend, BA will be operating all flights to and from London City airport and all long-haul flights to and from Gatwick airport in West Sussex.
A BA spokeswoman said: “We would normally operate around 400 to 450 flights on a weekend day. We’re hoping to be able to get around 65% of our passengers away this weekend.”
BA has arranged with more than 60 other airlines to take BA customers on their flights on the first strike days.
While some passengers whose flights have been cancelled will be travelling on other carriers, others have arranged to fly with BA at a later date and some have opted to get a refund.
“I’m really dismayed that Unite has decided to do this,” said Ben Wood, 37, of Newbury, Berkshire, a telecoms analyst who often flies with the airline.