From next year the airline said there will be a "small increase" in the number of seats on its Airbus A320 and A321 aircraft.
Reports suggest that this will amount to two extra rows, or 12 seats in total.
That will reduce average leg room for passengers by 1 inch per seat, to just 29 inches.
That amount of space will be the same as Easyjet planes, but one inch less than on Ryanair aircraft.
A BA spokesperson said the move would help to keep fares low.
Simon Calder, travel editor of the Independent, told the BBC the increase would bring the number of seats on BA planes to 180. That is the same as the total on Aer Lingus, Iberia and Vueling, which are also owned by BA's parent company IAG.
Airbus planes operated by Easyjet already have 180 seats, but that number will soon rise by six, while Ryanair will squeeze another eight seats on its planes, Mr Calder added.
Last November BA said it would increase the number of economy seats on its long-haul Boeing 777 aircraft by almost a fifth, from 280 to 332.
That means each row in economy class will have 10 seats rather than nine.
BA has 68 A320 planes in its fleet, along with 18 of the larger A321s aircraft.
British Airways plans to squeeze in more passengers on some planes it flies to European cities.