Family lawyers have attacked plans to write off #1 billion owed by to single mothers by fathers.
Birmingham lawyer Katherine Kennedy called the proposals "a huge injustice".
Ministers have abandoned plans for the Child Support Agency, which has its headquarters in Dudley, to track down the debts.
Instead, the Government will bring in new laws authorising the CSA to write the money off debts when there are "limited prospects of recovery".
But the proposals have been criticised by Resolution, which represents family lawyers.
It claimed the Government was creating a new system which would be "even more unfair and ineffective" than the existing one.
Ms Kennedy, of Birmingham-based law firm Mills & Reeve, said: "Write-offs on that scale would represent a huge injustice for thousands of families who have been failed so badly by the agency."
The Government had failed to think the reforms through, she claimed.
The decision means that about 130,000 single parents will never receive an average of #14,000 which they are owed in maintenance.
Critics have accused the CSA of giving up already on many cases.
Buried in the small print of the agency's most recent accounts, it classified #1.9 billion of its #3.5 billion debts as "probably uncollectable".
In many cases that means that the CSA has lost track of the errant father.
Resolution has put forward its own proposals to deal with the backlog of existing cases and to avoid backlogs occurring in the future.
They include allowing couples to agree their own arrears settlements, via the courts, and for the courts to have a greater role in assessing child support payments.
The Government plans will be published alongside proposals to abolish the CSA and replace it with a new body.
The national headquarters, in Brierley Hill, Dudley, employs 1,800 people, but Work and Pensions Secretary John Hutton has announced it is to close after 13 years.
Parents will be encouraged to make their own arrangements in future, so that a new streamlined agency can concentrate on chasing payments from fathers.
Stories of mistakes and inefficiency have dogged the Child Support Agency almost since its inception in 1993.
From day one, problems with its computer system put the agency under pressure as employees struggled to cope.
Debts of about #3.5 billion currently remain to be collected, a figure that campaigners say increases by #120 million each year.
The National Audit Office has warned that reforms introduced in 2003 had so far cost the taxpayer #536 million but had not produced significant improvements.
A damning report report revealed it now costs the agency 70p to collect just #1 in child support.
Conservatives claimed it would not meet its target for clearing a backlog of cases despite 1,000 extra staff.
The quarterly statistics show that it has cut the number of outstanding cases by just under ten per cent since March 2006. It has promised to slash the figure by 25 per cent by March 2007.