A total of 29 doctors due to start GP vocational training schemes in August received letters on 19 June informing them that the posts had been deferred until February.
The London Deanery blamed 'severe funding problems in the NHS' and 'extreme pressure' on training budgets.
Affected doctors were given a week to reply, stating whether they wished to accept the posts.
The letters said: 'We appreciate that deferring your post means that you will need to make alternative plans and that this may cause you difficulties.'
The group is among the last tranche of pre-foundation year one and two medics, aiming to become GP registrars from September 2008.
GPC chairman Dr Hamish Meldrum said he was appalled at the way the doctors had been treated: 'We are urgently seeking clarification both as to the reasons why this has occurred and also to see what employment rights these doctors have.'
One of the affected doctors, Dr Dinesh Sirisena said: 'It's disgusting. They are treating us like their property - they don't want us so they throw us away.'
Professor Neil Jackson, dean of postgraduate GP education at the London Deanery, said: 'We are confident that all affected doctors will start their training in February 2007 and we are currently working with the BMA to ensure that adequate support and careers advice is offered to all the affected doctors.'