Janet Roberts, director of Tendering for Care, raised the alert after noticing a flood of contracts open to third sector organisations.
Roberts has calculated that a record 73 contracts published in the first week of February related to services provided by voluntary and community groups. She said that this represented a rise of more than 50 per cent on the busiest week in 2007.
She told Third Sector that the contracts, advertised by government departments, quangos and local authorities, could pose problems for organisations used to a grant system.
"In a business culture you are subject to legal action if you cannot meet your commitments," Roberts said. "But umbrella bodies are not looking into how to support their members through that."
Seb Elsworth, head of policy at chief executives body Acevo, said: "We are growing our services in this area, including a legal contracts helpline and an in-house consultant to provide accurate advice."