US rapper Eminem. Photo / AP
"Eminem's publishers were not approached for permission to use any of Eminem's songs for this campaign advertisement," said Joel Martin, speaking on behalf of the publishers.
The National Party has rejected the allegations and says it purchased the music by the book.
Copyright lawyer Chris Hocquard, who founded Dominion Law in Auckland, said although the National Party thought it was doing everything right, the party could still be in the wrong.
"Unfortunately, from a legal perspective, the fact that they didn't think they were doing anything wrong doesn't mean they weren't doing anything wrong - it just means they can turn around and blame someone else later on."
Prime Minister John Key. Photo / Jason Oxenham
Mr Hocquard said if the National Party was found liable, it would likely to have to pay a five-figure sum to the publishers.
However, the National Party would likely be covered by an indemnity clause, which would be part of the agreement the party signed with music supplier Beatbox, based in Australia and Singapore.
If the party was found liable, it could go back to Beatbox and demand the company help pay any penalties, Mr Hocquard said.
"Your standard licensing agreement would have an indemnity clause in it, and a warranty would say you're entitled to use this music and it doesn't infringe on anyone else's rights.
"It doesn't absolve you from responsibility - but it does mean you can go after the person that caused it."
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When contacted today, Beatbox Australia said the company did not wish to make any comment.
National had purchased the music from Beatbox through Apra/Amcos - the Australasian body that acts as local agents for music licensing companies all around the world.
"It's almost like they went to the police - they went to who they considered to be the safest people in New Zealand to buy music from, and they bought music from them," Mr Hocquard said.
"They didn't go to some backstreet dealer - they went to the most reputable, safest, most knowledgeable licensing outfit in the country and bought it from them."
National's campaign chairman Steven Joyce said National had done everything by the book and he believed the legal action was aimed at getting money and free publicity.
Steven Joyce. Photo / Glenn Taylor
"I think these guys are just having a crack and have a bit of an eye for the main chance because it's an election campaign
" So good on them, but we'll be contesting it pretty seriously. We don't believe they've got any grounds at all and we suspect its politically motivated."
He said National had stopped using the music in its advertising about two weeks ago at about the same time the publishers contacted them.
"Nobody else seems to have had any trouble with it, it seems that picking on a political party might be flavour of the week."
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