The claim comes as the organisation urges PMS practices to join a legal support fund to fight unfair contract changes.
The NAPC has opened 'constructive' talks with the DoH, but expects guidance only once a new government is in place.
After 'an unprecedented number of requests for help', the NAPC has written to all PMS practices - some 40 per cent of practices in England.
GPs in the North East have warded off threats from a PCT by forming a defence fund, NAPC vice-president Dr Peter Smith told GP. One PCT had threatened to terminate contracts unless GPs signed up to a less favourable deal.
Dentists have also successfully challenged similar contract changes, the NAPC says.
But Dr Smith said that in some areas 'LMC advice had been inappropriate' and 'union support virtually non-existent'.
Some LMCs advised practices to 'immediately capitulate' to PCTs' demands, he said. But naming them might damage negotiations, he added.
The poor advice was due to 'a lack of confidence that we can win, and the fact that PMS does not come under the GPC's mandate', said Dr Smith.
The NAPC says there is no unilateral right to end contracts without good cause, and sets out legal advice on how to deal with unfair threats in its letter.
NAPC president Dr Johnny Marshall said his first aim was to assess the scale of the problem.
He stressed that many LMCs had been extremely useful and PCTs in some areas have been more co-operative.
Wessex LMCs chief executive Dr Nigel Watson said PMS reviews in the region had not led to disputes. 'PCTs in this area have been constructive and engaged with practices rather than threatening them.'