Cambridge CAB wanted criminal record checks for all its staff, from receptionists to trustees, because they might all have dealings with vulnerable people, or with data relating to vulnerable people.
"We met resistance from the CRB because it flatly refuses to check anyone who does not work directly with clients," said Rachel Talbott, chief executive of Cambridge CAB.
The charity has not been able to obtain checks for many staff, including IT workers and administrators who have access to sensitive personal information about vulnerable clients.
The CRB said its hands were tied by the legislation guiding its work.
A spokesman said: "The Exceptions Order to the Rehabilitation of Offenders Act 1974 sets out who can and cannot be checked. Obtaining a check on someone not covered by this Act would be illegal."
The spokesman added that the number and type of people who can be checked would be expanded in 2008, when a new vetting and barring scheme, established under the Safeguarding Vulnerable Groups Act 2006, will come into effect.
The Criminal Records Bureau has launched a free online tracking service that allows charities waiting for criminal record checks to trace their progress by entering a reference number and a date of birth.The system allows only one application to be traced at a time, but the CRB plans to allow multiple tracking later this year.