Labour deputy leader Grant Robertson is writing to the Electoral Commission asking it to take a fresh look at the Prime Minister's pre-election radio show.
The commission last week referred Radio Live to the police.
It had ruled that, while the show was not an election advertisment, because Radio Live retained editorial control, it was an election programme.
However, Mr Robertson says that email correspondence between the Prime Minister's office and Radio Live brings that into question.
He says John Key's office was heavily involved in the content of the programme, and wrote Radio Live's correspondence with the Electoral Commission.
Mr Robertson says the emails also show the office knew the programme might breach electoral law.
