"We should be pursuing these men and introducing penalties when they give inaccurate information or refuse to pay up, but instead the CSA has announced an amnesty," said Ms O'Neill, from Paisley.
"I can see the whole system crumbling now. How can they force men they are currently pursuing to pay up if they allow other men in the same position to get off?"
For Ms O'Neill the contoversy is just the latest example of CSA inepitude. Until May, her former husband paid £70-a-week maintenance for their two children, aged 15 and 12. She supplemented the family income with part-time work and family credit.
When the CSA insisted on reassessing the payments originally ordered through the courts it reduced his contribution to £9.09 a week. When she protested that her former husband, who now has a second family, had given inaccurate information she was told anappeal would take six months.
On the advice of her solicitor she contacted a newspaper. Its subsequent investigation speeded up the appeal considerably and the payments were reassessed at £61.
"But I haven't received a penny since," said Ms O'Neill. "The CSA has not bothered to collect. Now my ex-husband is saying he has lost his job. There are arrears of £600."
She added: "This new announcement makes official what is already the practice ... It's really a victory for all those absent fathers who have lobbied and organised in a way impossible for single mothers too busy caring for their children."