The Labour Party leader, David Cunliffe, is accusing John Key of being inconsistent in the way he has treated Maurice Williamson and Judith Collins.
Mr Key accepted the resignation of Maurice Williamson from his ministerial portfolios last week, after it was revealed he had rung a senior police officer to ask about a criminal investigation into a Chinese-born businessman.
But Ms Collins retained her ministerial posts despite intense criticism over her dealings with the dairy exporter Oravida.
Mr Cunliffe told the Sunday Morning programme he would be questioning Mr Key's discrepancies and double standards when the House resumed sittings.
Separately, Mr Key dismissed the idea that it had been a bad week for National, and said Labour's loss of Shane Jones was more serious.
Speaking at a National party regional conference in Auckland on Sunday, Mr Key said there would be good and bad weeks for the Government in the lead-up to the election.
But he said Mr Jones's resignation meant Labour had lost its only MP with an interest in economic growth.
He alleged both Labour and the Greens were anti-growth and anti-jobs, and the contrast with National would be highlighted in the election.
Mr Key warned National party members against complacency in the election.