The Health Bill is expected to move to the Lords next month after MPs backed it last week.
Talking to GP, Labour peer Lord Rea of Eskdale said the Lords would seek a 'number of amendments'. He said concerns would be raised about clinical commissioning, with some peers wanting to see far more detail on plans for CCGs.
'If this whole thing is going to continue, then the definition, function and the catchment areas of CCGs will need to be much better defined,' he said.
'At the moment we have too many CCGs of variable sizes.'
Lord Rea said the minimum population size for CCGs should be set at around 250,000 patients, although he said this would not have to be 'strictly adhered to'.
Labour peer Lord Hunt of Kings Heath said there were 'bound to be discussions' about the accountability arrangements and membership of CCGs. 'If CCGs have got all that dosh they have to be accountable for it,' he said. 'CCGs are given so much responsibility and there ought to be more lay involvement.'
Lord Hunt said other key areas for discussion would be the health secretary's responsibility for the provision of a comprehensive health service, as well as debates on the market in the NHS. 'There are concerns about whether the plans are the thin end of the wedge for full privatisation,' he said.
GPC deputy chairman Dr Richard Vautrey said it was 'unlikely' that the Lords would make significant amendments to clinical commissioning proposals. But he added that the Lords could make changes to the accountability and governance arrangements.
'They could also mitigate some of the complexity that's crept into the Bill,' he added.