British Airways (BA) has assured customers proposed strike action by the Unite union will have little effect on flights.
The strike dates are set for January 10 and 11.
After confirming flights from London Gatwick and London City airports would operate as normal, BA said a "very small number" of flights to and from Heathrow would be merged.
This means some customers are being moved to earlier or later flights in the day from their original booking.
Approximately 200,000 customers will fly with the airline over the two-day period, and BA said those affected by the changes are being contacted with their options.
"We urge Unite to abandon its strike plans which are serving only to cause anxiety among our mixed fleet cabin crew colleagues who do a tremendous job for our customers," the company said in its statement.
On 22 December, a two-day walkout scheduled for Christmas Day and Boxing Day was called off after talks between Unite and BA. Union members then rejected a new pay offer.
Unite has now accused BA of refusing to extend a mandate for the strike vote, saying union members are legally required to strike within 28 days of voting unless granted an extension.
“British Airways is needlessly provoking strike action by refusing to extend the mandate of the strike ballot and allow meaningful talks to take place," said Unite national officer Oliver Richardson.
BA today said they are open to further dialogue with Unite.