British Airways risks incurring the wrath of its passengers by adding £240 (€378) to the cost of a long-haul return flight if a passenger puts two bags in the aircraft's hold.
From next Tuesday, BA passengers will also pay an extra £120 on short-haul return flights and £60 on domestic return flights if they take two bags on to the plane.
Many of the airline's passengers are only expected to learn of the new charges when they check in at airports next week.
The rule means that customers will be able to put a bag with a maximum weight of 32kg in the hold - reducing to 23kg from September 30th.
They will have to pay the extra charges even if the combined weight of the two bags is below the limit. BA's website said the new charging system aimed to introduce a "single allowance system based on the number of bags that can be checked in".
It said: "Our vision for London Heathrow Terminal 5 is to create the best possible airport experience before you fly. "With this in mind we have announced a new simpler checked and excess baggage policy, which will come into effect on February 13 th, 2007."
According to the Daily Telegraph, BA confirmed that its sales staff were instructed not to tell customers in advance when they booked their tickets.
A BA spokesman told the paper: "They will tell people if they ask about baggage policy. But it is on our website." Until September 30th, passengers will receive a discount if they pay in advance online - the extra charge per bag will be £168, £84 and £42 for return long-haul, short-haul and domestic flights respectively.
However, paying in advance - through BA's website - is not available on certain routes, and some credit cards cannot be used as payment methods.
Passengers will be able to carry one piece of sporting equipment on to the plane as well stowing one bag in the hold, the website said.