The airline said in a statement that it has “regrettably” become necessary to further reduce its operations.
The Government has introduced a slot amnesty, which enables airlines to temporarily hand back without punishment any take-off and landing slots they do not have the resources to use.
Under normal rules, carriers lose slots if they do not use them.
The aviation industry is suffering major disruption as a surge in demand for travel coincides with staff shortages across roles such as airline crew, ground handlers, airport security staff and air traffic controllers.
Thousands of flights have been cancelled and many passengers have been forced to wait for several hours in long queues at airports.
In May, British Airways announced that it would cancel 10% of flights between April and October in an attempt to avoid having to axe flights on the day of departure.
But the latest cancellations take this figure to around 11%.
The carrier 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.
“We’re in touch with customers to apologise and offer to rebook them or issue a full refund.”
The airline welcomed the slot amnesty, saying it is “making it easier to consolidate some of our quieter daily flights to multi-frequency destinations well in advance, and to protect more of our holiday flights”.
Heathrow ordered 30 flights for the morning of June 30 to be cancelled at short notice in a rare “schedule intervention” because it would have been unable to handle the passengers.
British Airways workers based at the west London airport are deciding on strike dates which are likely to be during the peak summer holiday period.
Members of the GMB and Unite unions, including check-in staff, voted in favour of industrial action in a dispute over pay.