The travel plans of hundreds of passengers flying between the UK and Spain were thrown into disarray yesterday through a strike called by a pilots' union.
Spanish carrier Iberia had to cancel five flights between London and Spain - three to Madrid and two to Barcelona.
And further Iberia flights between Heathrow and Madrid and Barcelona are set to be axed, with the strike due to carry on until Sunday.
Iberia and British Airways jointly market some London-Spain flights under a code-sharing agreement.
A BA spokesman said: "We are working on contingency plans to ensure that as many British Airways customers who are booked on Iberia flights can get to their destinations.
"We would urge any BA customer who has booked a flight between Heathrow and Madrid/Barcelona on July 10, 11 and 12 to contact BA if they booked their ticket direct from the airline or their travel agent to see if their flight is affected and how they can be re-accommodated."
A Heathrow Airport spokeswoman said: "We are advising passengers to contact their airline before travelling."
Birmingham International Airport said that its flights to Barcelona and Madrid were unaffected. The Iberia pilots are striking over fears of job losses. In all, around 240 Iberia flights are likely to be cancelled each day.