Ross Clark, a partner at law firm Hempsons, told a National Association of Primary Care conference in London last week that consortia budgets would be substantially dented if they were forced to take on PCT staff.
He said many PCTs were assigning commissioning staff to consortia because they knew that once GPs take over commissioning in 2013 they would be obliged to take on these staff under Transfer of Undertakings (Protection of Employment) regulations (TUPE).
This will mean that they have to honour PCT salaries and terms, as well as offer similar pensions, he said.
He said: 'PCTs are assigning staff to commissioning support duties. You might say: "Fantastic, that's really helpful," but you have got to understand the application of TUPE. When it comes, TUPE applies. That's the danger. You can't get out of it. It will transfer employees across.'
Mr Clark warned that having to take staff on under TUPE arrangements could leave 'big dents' in consortia budgets.
He urged consortia to be wary of PCTs assigning staff and to push on with their development to ensure they were not undermined by PCTs. He said: 'The trouble is that PCTs are ahead of the game. They have seen what's coming, they are organised.'
GP consortia were yet to become fully formed and were not aware of the risks of TUPE legislation, he said. 'The issue here is not horrible PCTs here to stiff you. It's you are behind the timeline. By the time you catch up it could be too late.'
GP revealed earlier this month that PCTs were failing to give consortia the £2 per patient development funding pledged by the DoH in cash, and instead offering part of the fee in the form of management support.
GPC deputy chairman Dr Richard Vautrey said consortia should 'tread carefully' to ensure they avoid employment issues in the future.