Govt spent $565,000 for $6,000 child debt

A federal government department has spent $565,000 pursuing a father over a disputed $6,000 child support debt.

The Department of Human Services defends the cost, saying it's all about clarifying a legal principle.

Independent senator Nick Xenophon raised the case during a Senate estimates hearing in Canberra on Thursday.

The father has spent four years disputing child support agency orders requiring him to pay $6,000 to his ex-wife, he says.

"A fortune is being spent against an unrepresented father," Senator Xenophon said as he quizzed department officials.

The department insisted the case was worth pursuing because it would help it administer the entire child support system.

"This is not just about a $6,000 assessment, it's about a much broader range of issues," department boss Kathryn Campbell said.

One of the reasons for the big cost was that the department was also paying the man's legal costs as it sought "clarity".

The commonwealth won the first round of the dispute, but has now filed a case in the Administrative Appeals Tribunal to block the father from receiving key departmental documents.

The department argues legal professional privilege applies to its refusal.

Human Services Minister Marise Payne said she would look into the matter after being asked to ensure the man won't have to face further legal costs.