The National Party ran a television ad 186 times that used the song "Eminem Esque" during its successful 2014 election campaign before pulling the ad off the air.
The music used in the National Party ad was called Eminem Esque, copying and exploiting the original award-winning music.
"Eminem Esque is strikingly similar to Lose Yourself with minimal discernible differences and objectively, it was created to "sound like" Eminem and Lose Yourself..."
National has now said it is considering legal action against the suppliers and licensors, while Eight Mile Style has a case for third party liability which was held back until there was a decision on its case against the National Party. She said it was no coincidence the composer of "Eminem Esque" had the music to the original in front of him when he wrote his song.
Cull stopped short of hitting up the National Party for additional damages, stating that they had acted on professional advice that led to them including the song in the advertisement.
The National Party was disappointed with the ruling, party president Peter Goodfellow said.
"The music was licensed with one of New Zealand's main industry copyright bodies, the Australasian Mechanical Copyright Owners Society [AMCOS]".
"'Sound alike' tracks are often used in advertising to be reminiscent of well-known original music, while avoiding appropriate acknowledgement and payment for the use of the original piece". He said the celebration brought the music in proper belief from an Australia-based library that had bought it from a USA supplier. It was found by a New Zealand court to have "substantially copied" his 2002 hit Lose Yourself.
The publisher had exclusive control over the song and rarely gave permission for its use in advertising.
He said the party was considering its next steps and already had lodged a claim against the suppliers and licence holders of the Eminem Esque track.