Calls for the Deputy Prime Minister to be disciplined for calling Karel Sroubek's estranged wife "a National Party informant".

Winston Peters made the comments last week, while answering questions on behalf of the Prime Minister.

It's understood her new partner is a member of the National Party.

But Justice spokesperson Mark Mitchell says it's outrageous Peters has attempted to discredit her very real concerns.

"She came to the Opposition through a retired Labour minister, and it is my job as opposition to make sure the Government is held to account. And now she's got the deputy Prime Minister making cheap political attacks and shots at her."