Apple has criticised a French law that could break the locks tying songs from the iTunes store to iPod players.
The French law could hit operators of closed download services
In a statement Apple said that if the law were passed it would result in "state-sponsored piracy".
The law to open up all online music stores is due to go to France's upper house of parliament for final approval.
The French government said the law was drawn up to ensure no single company dominated the fast growing music download market.
On Tuesday French lawmakers voted 296 to 193 in support of a law that would stop Apple, plus any other firm selling music downloads, using proprietary software to limit what people can do with tracks they have bought.
The draft law now goes to the Senate - the upper house of the French parliament - for final approval before it gets on to the statute books.
If the draft becomes French law it will mean that firms selling music must make available information about the software they use to stop songs being copied - so-called Digital Rights Management (DRM) systems.
This would enable tracks downloaded in one format to be changed and played on any other device. France said it hoped other European nations enacted similar laws.
The law allows any interested party to request information about the DRM system so the protected files can be made interoperable.
In a response issued after the law won initial approval, Apple said: "If this happens, legal music sales will plummet just when legitimate alternatives to piracy are winning over customers."
But, it added, the law could prove a boon for Apple and its popular iPod music players.
Said Apple: "iPod sales will likely increase as users freely load their iPods with "interoperable" music which cannot be adequately protected. Free movies for iPods should not be far behind in what will rapidly become a state-sponsored culture of piracy."
Analysts have said if the French law is enacted it leaves Apple with a choice between shutting down the iTunes store in France or complying. The loss of revenue from a closure might not be too heavy as market reports suggest that iTunes sales in France make up only 5% of the global total.
Jonathan Arber, analyst at market research firm Ovum, said: "This is potentially a big blow for Apple, whose iTunes/iPod business model is built on its very lack of interoperability with other devices and services."
"This could force Apple to withdraw from France, or certainly rethink its strategy in the country."
But, he added, the intricacies of how, and if, the law will be enacted have yet to be confronted.