British Airways said seat charges will give customers "more control"
British Airways passengers will have to pay to choose their seats before they travel from October, the airline says.
The charges will affect those seeking to ensure they sit together on a flight and people with a preference for window, aisle or emergency exit seats.
Prices range from £10 per person for European economy flights, to £60 for long haul trips in business class.
Consumer group Which? said it was "disappointing to see British Airways jumping on the bandwagon".
BA said it would "give customers more control over their seating options". The new charges will come into force on 7 October.
The airline currently allows passengers to reserve seats in the 24 hours prior to departure.
The new charge - aimed at passengers wanting to reserve seats earlier than this - will be £20 on long-haul economy or short flights in business class, while a seat in an emergency exit row will cost £50.
This can be booked between 10 and four days before take-off.
A BA spokeswoman said: "Customers frequently request specific seats, but in the past we've only been able to confirm them 24 hours in advance or on the day.
"We know people want to secure them in advance and have real control over their flying experience. This will allow them to do that."
Rochelle Turner, head of research at Which? Holiday, said travellers had become used to budget airlines charging them for a service that used to be included in the "headline price".
"We know from our members that people really don't like these extra charges - they'd much rather see a headline price that includes everything," she said.
"BA is still giving some people the chance to reserve their seat for free in the 24 hours before departure, but if you aren't quick enough off the mark, you could find yourself sitting on the other side of the plane from your family or partner.
"It's no way to start a holiday."
The move comes as the airline attempts to bolster its balance sheet after a £401m loss in the last financial year.
And it follows BA's decision to cut luggage allowances and abolish free meals on short flights.