The suit revolves around the $100m investment made in the now-defunct Napster song-swapping service by Bertelsmann, itself a member of the Big Five record companies through its BMG subsidiary.

France's Vivendi Universal is already a party to the suit, which was first announced in February.

"By investing both millions of dollars and management resources in Napster - which was an illegal enterprise built on the unlawful distribution of copyrighted works - Bertelsmann enabled and encouraged the wholesale theft of copyrighted music," EMI said in a statement.

Whose fault?

EMI, which has suffered from heavy losses and lacklustre performance in recent years, is the third biggest of the Big Five, the other members of which - aside from BMG - are Universal, Sony and AOL Time Warner.

It is also - with the exception of Bertelsmann's investment in Napster, now owned by CD-burning software vendor Roxio - the one which has done the most to tackle the issue of online music delivery.

But like its fellows, it has consistently blamed services like Napster, and those still running such as Kazaa and Gnutella, for the slide in CD sales in recent years.

Critics, on the other hand, say the blame lies as much with the record companies for concentrating resources on a small number of big artists rather than on promoting lesser known artists, and keeping CD prices artificially high.

Just as important, they say, is the increasing homogenisation of radio as more and more stations are owned by large corporations, reducing the variety of music on offer and thus cutting into consumers' options.