Shadow Home Office minister Julian Brazier has called for price increases brought in by the Criminal Records Bureau this month to be dropped.
Brazier is opposing the Government's statutory instrument, required to authorise the price increase, saying that it is unjustifiable in the face of continued inefficiency and a backlog of 50,000 uncompleted checks.
If the statutory instrument is blocked, the price increase could be overruled.
The Conservative MP has also written to the Auditor General, Sir John Bourn, who has responsibility for auditing the accounts and checking the efficiency of government departments, asking him to investigate the CRB.
However, the CRB says that the service is now running smoothly and that the backlog has been whittled down to less than 4,000."Only 5 per cent of checks are more than six weeks old," said Mark Favager, communications manager at the CRB. "Their figures are inaccurate."