Wellington, May 1 (IANS): US rap artist Eminem is suing New Zealand's ruling National Party over a a track it used for a campaign ad in 2014, the media reported on Monday.

The rapper said the song, used in the party advert, was an unlicensed version of "Lose Yourself", one of his biggest hits and also the winner of an Academy Award for Best Original Song in a Movie category, along with two Grammys, the BBC reported.

Lawyer Gary Williams for Eight Mile Style, the company representing Eminem, told the High Court in Wellington on Monday that the National Party infringed copyright by using the song, or a substantial reproduction of it, reports the New Zealand Herald.

"The song 'Lose Yourself', is without doubt the jewel in the crown of Eminem's musical work," Williams said in his opening statements to the court.

Even if the party only authorised the infringement, that in itself would be a breach of copyright, he said.

Williams said it did not matter if the song's lyrics were not used.

He said there were three layers of copyright, covering lyrics, musical composition and then the sound recording itself.

The two tracks were played in court.

But the party's lawyers argued that it was not actually "Lose Yourself", but a track called Eminem-esque which they bought from a stock music library.

The National Party denies being responsible for any copyright infringement, reports the BBC.

Defence lawyer Greg Arthur said copyright was "not in any way proven by the name given to a piece of music".

The case is expected to continue for six days.