The move comes as the DH stepped up plans to offer a list of 39 services to any qualified provider from next autumn and follows a report from financial analysts that said the NHS reforms would create a £20 billion opportunity for the private sector.
Medical Practitioners' Union (MPU) president Dr Ron Singer said some CCGs have taken legal advice over including clauses to limit the role of the private sector.
'There is a move afoot to tweak CCG constitutions in favour of looking towards the NHS as much as possible,' he said.
GP commissioners in London and south-west England are understood to be investigating how to block private providers.
Some are working to adapt a BMA 'voluntary charter' published earlier this year, which includes clauses rejecting imposition of any qualified provider 'from external sources' and contracts that impose conditions of commercial confidentiality.
Some CCGs are under pressure from member practices to limit the role of private providers through their constitutions. For CCGs to be authorised, their constitutions must be signed by all member practices.
NHS City and Hackney CCG, which is in the third wave of authorisation, met member practices last week to discuss its constitution.
Hackney GP Dr Jonathon Tomlinson said the CCG board was 'very sympathetic' to GPs' concerns about privatisation. 'The constitution should say that we will not contract with any provider who has been found guilty of fraud or uses tax-avoidance schemes.
'Ideally I'd say no to shareholder-owned companies and anyone without a track record of healthcare provision locally but we may not want to limit ourselves that severely.'
Pressure groups in Gloucestershire have also taken legal advice in a bid to challenge the any qualified provider policy.
Keep Gloucestershire's NHS Public said it had legal advice that not putting services out to tender would not breach EU procurement law.
Dr Singer said that the move by CCGs was 'calling the government's bluff' on its commitment to localism.
He warned that an influx of private providers could lead to the fragmentation of services.
National Association of Primary Care chairman Dr Charles Alessi said CCGs' responsibility was to commission the best services, and that they should consider private providers where appropriate.