The benchmarking report said overtime working, often on a compulsory basis, posed serious problems in a number of services.
It acknowledged that some element of overtime would always be necessary to provide a cost-efficient service and to cope with valleys and peaks of work output.
However, it said: "The Body believes that the unduly high level of overtime currently being worked at enhanced rates of pay in some sectors is unsustainable".
Prison officers and gardaí are among those for whom overtime is compulsory, and both groups now believe this affected the pay awards recommended for them by the benchmarking body, 4 per cent and 5 per cent respectively.
The general secretary of the Prison Officers' Association, Mr John Clinton, said he believed prison officers had been penalised as a result of their overtime earnings. "It would appear the fact that we are a group of compulsory overtime workers was taken into consideration. We seem to have been penalised for working overtime which is compulsory," he said. Overtime work in prisons cost £38 million in the year 2000.
Mr George Maybury of the Association of Garda Sergeants and Inspectors also said the body appeared to have taken excessive account of overtime payments to gardaí.