The Federal Opposition says the Indigenous Affairs Minister must now resign, after admitting it was his voice on a taped conversation about a prominent Aboriginal leader.

But Philip Ruddock says he has done nothing wrong.

On the tape, Philip Ruddock briefs a journalist about police investigations into ATSIC Commissioner Ray Robinson.

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

Philip Ruddock has previously asked Mr Robinson to explain some of his business dealings and may have to consider whether Ray Robinson is dismissed from his ATSIC position.

Labor's Bob McMullan says there is a perception Mr Robinson would not get a fair hearing.

"Philip Ruddock should absolutely step down as Indigenous Affairs Minister," he said.

"One of the most crucial matters in the portfolio - that is the reform of ATSIC - is a matter he is now incapable of handling."

Philip Ruddock has rejected the bias claims, and says he will not be compromised in any decisions he makes about Ray Robinson or ATSIC.