Radio Live have indicated they may mount a legal defence against the ruling.
The bulk of nzherald.co.nz readers feel the Prime Minister should apologise for what many see as an error in judgement.
McHaggis, from the Hibiscus Coast believed Mr Key was wrong to DJ the radio slot.
"Key knew full well that his appearance on Radio Live, was an election promotion, given the timing of the broadcast," they wrote.
"It was blatant electioneering done in an indirect way, promoting Key and his National government! Even more so, as other political parties were obviously not given the same opportunity."
Lily agreed.
"Key definitely should be held accountable for his in-your-face actions. It was a blatantly obvious one-off electioneering broadcast. This man totally lacks integrity on any level."
Jonman said the argument the show was not political because he didn't talk politics does not wash.
"It's political simply because he is a prominent politician - and it really doesn't come any more political than being the Prime Minister. So, cough up the fine, John. And wise up."
The Hooded Finger believed he should apologise - on rival station Radio New Zealand.
"He always dodges appearing on that station because they actually do want to examine his 'politics'."
Gandalf, from St Heliers felt anything less than an apology would be hypocritical.
"National were critical of labour pushing the electioneering rules. There's no difference so apply the same standards to yourselves.
However a number of readers backed Mr Key's appearance behind the microphone.
"Wasn't he on the radio talking about his cat? Didn't he specifically say he wouldn't be talking about politics. He went out of his way to do the right thing and was found "guilty" on a technicality," YouKnowItsTheTruth wrote.
Ant argued the majority of New Zealanders did not listen to the programme and had not even heard about.
"For the opposition party to complain about it now is disappointing to say the least as it highlights the fact they apparently have nothing more pressing to attend to. Also for the police to be wasting their time on this so called illegal radio programme is something bordering on the ridiculous."
MBC disagreed the show was electioneering.
"Thad advice at the time that it would be OK. I saw on TV that Key started the broadcast with a no electioneering statement and kept it so. Just because the ruling went the other way after months of consideration doesn't mean that they (the commission) are right. How can any one decide in advance what the commission took 3 months to decide?"
