London's mayor will be issued with legal proceedings in an attempt to allow Save The Trafalgar Square Pigeons group to continue feeding the birds.
The mayor wants to get rid of pigeons from Trafalgar Square
The group said mayor Ken Livingstone had gone back on an agreement to allow it to feed the pigeons every morning.
But a spokesman for the mayor said animal rights activist were feeding pigeons on the square's north terrace, which is outside of its jurisdiction.
As a result there is no need to feed the birds in main square, he added.
The Save The Trafalgar Square Pigeons group said withdrawing the scheme means the mayor has broken a legally binding contract.
The campaigners are seeking an order of specific performance which would force the Mr Livingstone to abide by the terms of the agreement, which has been in place since 2002.
They also claim the mayor failed to keep a promise to pay £3,000 towards the cost of the feed.
The amount of food given by the group has gradually been reduced to stop excessive breeding and allow a natural reduction in numbers.
A spokesman said their solicitors will be attempting to begin proceedings at Central London County Court on Monday.
The spokesman for the mayor said: "Since the introduction of a byelaw banning unauthorised pigeon feeding, and other methods such as the use of a hawk, there has been a reduction in the numbers of pigeons on Trafalgar Square so that the space can be used properly by the public.
"As there is persistent and anti-social feeding by pigeon-rights activists on the north terrace of the square, which is controlled by Westminster City Council and currently does not benefit from the protection of the byelaw covering the main part of the square, there is simply no case for feeding the feral pigeon colony in the Trafalgar Square area."
Earlier this year it was revealed that the mayor's quest to clear the central London square of pigeons has cost at least £226,000.