Peter Lilley, Secretary of State for Social Security, and Ros Hepplewhite, chief executive of the agency, are to be called to give evidence to the social security select committee in the next few weeks.
The committee decided yesterday to hold an inquiry because of the volume of complaints received by MPs during the summer. Since the agency began work in April it has taken on 500,000 cases and had sent out 20,000 new assessments by the end of August.
Many absent fathers who were not previously paying anything towards the upkeep of their children are unemployed or on low incomes and so will be exempt from paying. A leaked memorandum showed staff were being encouraged to target middle-class parents who already had court orders and were therefore easiest to trace, to help meet the Government's target of saving pounds 530m this year.
Frank Field, the committee's Labour chairman, said: 'We remain supportive of the Child Support Agency and the reforms, but we are going to look into how it operates in practice. Given the enormous number of letters we have had we know what the grievances are and we will use these as the basis for our questioning on the operation of the scheme.
'We will focus on things we feel are unfair. There are clean break settlements in which fathers have handed over the house or equity from it in exchange for low maintenance payments and these payments are being overturned. We warned this would be a real bone of contention but the Government rejected taking this into account.
'There are fathers who have remarried and are having to support stepchildren because their natural father is unemployed or on low income and does not have to pay. There is also a case for phasing in increased payments over, say, two years to give fathers a chance to readjust their finances.'