Charities are facing "another Criminal Records Bureau disaster" under proposals for another vetting scheme to protect vulnerable individuals.
The English Community Care Association and Leonard Cheshire have both expressed concerns in their responses to the consultation, which is being run jointly by the Department for Education and Skills and Department of Health.
The proposals arose out of Sir Michael Bichard's inquiry into the murders of Holly Wells and Jessica Chapman in Soham in 2003.
The new checks will be in addition to the existing Protection of Vulnerable Adults list and criminal records checks to offer a comprehensive, centralised system to prevent inappropriate staff or volunteers working with children or vulnerable adults.
Clare Smith, director of human resources at Leonard Cheshire, welcomed the emphasis on security but warned: "Unless there is a second round of consultation on the details of the proposals, it could lead to another Criminal Records Bureau disaster - when the system didn't work for a year."
She said there has thus far been no talk of costs, and added that it was essential that voluntary income did not get swallowed up by bureaucracy.
She also raised concerns that the proposals contain loopholes that could be exploited. An employer could use the new system, for example, to run their own check on a prospective employee - if they are not barred, the employer would no longer have to apply for criminal records checks.
Smith said: "It may be that only serious offences are listed and people, such as someone with a drink-driving offence, could slip through the net. But if you're employing someone to drive a minibus, this is something you would need to know."
Martin Green, chief executive of the English Community Care Association, the largest representative body for community care in England, said: "It is essential that the new system has a realistic lead-in time, is efficient and easy to comprehend, and doesn't lead to any additional regulation or costs."
A spokesman for the DfES said the scheme is still at the developmental phase and that the details, including fee structures and the business processes, have yet to be decided.