In an official submission to the work and pensions select committee last week, union officials warned that the new IT system, which was supplied by EDS, is causing "significant problems" for both customers and staff.
"The basic problem is that the IT system has not bedded in at all and is preventing CSA staff from doing their job properly," it said.
Designed to help implement child support reforms, the system went live earlier this year, nearly 12 months behind schedule. But the PCS, which represents the majority of CSA staff, said that, since 3 March, less than 100 cases out of 60,000 processed on the new legislation have resulted in the parent receiving at least one maintenance payment.
The PCS said the new system has not been available for much of the working day. The report also claimed the system is slow.
The project hit the headlines last year when its go-live date was delayed to allow further testing by EDS. A statement from the company last summer said, "The system is highly complex and more sophisticated than originally anticipated due to a change in government requirements."
A spokesman for the Department for Work and Pensions said the government is working with EDS to resolve the "teething problems" in the system.