The Government may face a backbench rebellion over plans to privatise the Probation Service.
The union Napo claims that up to 45 Labour MPs will support an amendment to significantly alter the Offender Management Bill.
This will allow private companies and voluntary groups to run probation work.
Napo claims that official figures show more is bring spent on bureaucracy in the National Offender Management Service (Noms) than in the whole of frontline probation work.
The union says that Treasury figures reveal £899 million was spent on centralised and regionalised bureaucracy, compared with £832 million for the whole of the Probation Service in England and Wales.
The crucial amendment, by Labour rebel Neil Gerrard, seeks to exclude core probation tasks from the effects of the Bill.
The Government has tabled another amendment, which would exclude the writing of court reports on offenders from the provisions of the Bill, but this was unlikely to pacify opponents.
Napo assistant general secretary Harry Fletcher said: "The Bill will destroy the National Probation Service and introduce a pseudo-market.
"The measures will erode local accountability, undermine public protection work, and will no doubt result in a rise in re-offending rates."
