Indigenous Affairs Minister Philip Ruddock has admitted it is his voice on a tape-recorded conversation which discusses the financial dealings of ATSIC commissioner Ray Robinson.

On the tape, Mr Ruddock briefs a journalist about police investigations into Mr Robinson.

Mr Robinson says it is proof that Mr Ruddock is biased against him.

Mr Ruddock says he now realises it is his voice on the tape, but denies he was trying to undermine Mr Robinson.

"The interview was primarily about investigations that were then current and those investigations had already been underway," he said.

"They'd been the subject of some media comment already and I was in effect giving a status report."

Earlier, Labor's Bob McMullan said if the tape is genuine then it shows the Minister is trying to manipulate media coverage of Indigenous issues.

"If the tape's authenticated, Philip Ruddock has prejudiced his capacity to pursue the necessary task of reforming ATSIC," he said.

"If this tape's authentic, he should step down as Minister for Indigenous Affairs."