Labour Party leader Phil Goff says is too close to the election to have the Prime Minister host a radio programme and not extend the offer to other party leaders.
The main opposition party has lodged complaints with the Broadcasting Standards Authority and the Electoral Commission over the programme featuring John Key on RadioLIVE last Friday.
Mr Key hosted an hour on the station where he interviewed a range of people but said he would not talk about party policy. However, Mr Goff says it was still an hour-long promotion for the Prime Minister.
Labour's general secretary Chris Flatt believes Mr Key hosting a programme so close to the election was in breach of the Broadcasting Act and the Electoral Act.
Mr Flatt says it breached a prohibition on paid election programmes and the election programme's code of broadcasting practice.
The Prime Minister says he does not know if his office sought advice before he appeared on the show, but says it is a matter for the station.
A spokesperson for Mediaworks, the company that owns RadioLIVE, says the show was neither election programming, nor election advertising.
Jana Rangooni also rejected a suggestion from Labour that the invitation to Mr Key was linked to financial assistance given by the National Government to MediaWorks in the form of a deferred licence payment.
Mediaworks says the Labour Party is entitled to check it acted lawfully, and while that process is underway, it will not comment further.
The election will be held on 26 November.