The National Party says it believes Labour leader Helen Clark is being briefed before the release of secret recordings of its MPs.
Another secretly-taped conversation with National's deputy leader Bill English has emerged in which he expresses concerns about US presidential candidate Barack Obama's approach to international relations.
Mr Key says the context of the statements are not known and the tapes could have been doctored.
But he says he does not share the views expressed by Mr English on the tapes.
Mr Key says he is confident Labour's "fingerprints" are on the tapes.
"I'm campaigning to become Prime Minister of New Zealand to lead a government that's going to focus on those core issues of education, health, law and order and the economy and I'm just not going to get in the mud and roll around with a pig, because if you do both parties come off looking pretty bad.
"I'm going to leave the Labour Party to the muckraking."
Mr Key would not be drawn on who he was referring to as a pig.
