The industry's apprehension comes as Rob Zombie and White Zombie, Whitesnake and Dave Mason have launched a series of class-action lawsuits against Universal Music in the US arguing their contracts have erroneously counted digital downloads as sales.

The rock acts argue Universal should have specified any digital activity as licensing agreements, which would attach a significantly higher royalty payment.

Their move comes two months after Eminem's producers successfully argued that the same major violated their contract by counting digital downloads ...