The wave of cancellations made over the past weeks will affect tens of thousands hoping to jet off this summer from Heathrow and Gatwick.
The industry has been struggling with staff shortages as demand for air travel rebounds.
British Airways had already removed 10% of scheduled flights between April and October, but said that "regrettably" more reductions were needed.
A spokesperson from the airline, which is the UK's largest, said: "We took pre-emptive action earlier this year to reduce our summer schedule to provide customers with as much notice as possible about any changes to their travel plans.
"As the entire aviation industry continues to face into the most challenging period in its history, regrettably it has become necessary to make some further reductions."
The carrier said it was in touch with customers to "apologise and offer to rebook them or issue a full refund".
The wave of cancellations comes ahead of Friday's deadline, announced last month by the Department for Transport (DfT), for an amnesty to give airlines a short window to hand back airport slots in the summer season they are not confident they will be able to operate.
BA is expected to announce further cancellations over the summer ahead of the deadline.
Airport slots provide airlines with the authorisation to take off or land at a specified time on a specified day. In usual circumstances, the carriers risk losing the slots - and taking a hit to their business - if they cancel flights.
On Wednesday, British Airways was also affected by a rare "schedule intervention" by Heathrow Airport.
Heathrow asked airlines to cut 30 flights from their Thursday morning schedules, as more passengers were expected than it could deal with.