The letter, from NHS Haringey, said that 2009/10 is a 'difficult year financially'. It goes on to say that the PCT is considering plans to amalgamate a range of services into three core LESs.
Londonwide LMCs joint chief executive Dr Michelle Drage said: 'The PCT has informed GPs that it will be stopping all LES payments with immediate effect.'
GPs have been invited to continue with the work for free if they wish, she added.
Most of the LESs involve contracts that run until the end of the year, and are worth 'millions of pounds' to GPs across the area, Dr Drage added.
Londonwide LMCs said Haringey PCT had not responded to concerns it had raised over GPs' incomes.
A response from Haringey PCT was unavailable at the time of going to press.
Uplifts to GP pay agreed for the 2009/10 GMS contract were to be spread across services including LESs.