A Nordic-led effort to force Apple to make its online store compatible with rival companies’ digital music players has gained more support from consumer groups in Germany and France.

Songs downloaded using iTunes can only be played on Apple’s iPods but the group wants an open iTunes that’s compatible with players such as Windows Media System. Likewise the iPod does not natively support any copy-protected tracks sold at non-Apple music stores such as Napster.

In June last year it was ruled that the Apple iTunes service had broken consumer protection laws following claims from consumer agencies in Norway, Denmark and Sweden. Norwegian Consumer Ombudsman Bjoern Erik said that it’s not good for the music industry if music is locked into one system. Apple officials have met Nordic regulators concerning the complaints on at least two occasions.

Those who have also joined the effort late last year include French lobby group UFC-Que Choisirm, German consumer group Ferbraucherzentralen and Finland’s Kuluttajavirasto.

A French law was also put in effect in August last year in a bid to force Apple to make its iPod player and iTunes store compatible with rival offerings. Apple argued that opening its formats could lead to further pirates.