Watch out, Box.net users—if the RIAA suspects you of mixing in music files with those boring Word and Excel documents that you use for work, you may be in for a legal battle. The RIAA has apparently turned its sights upon the business-oriented file-sharing service after filing a declaration in California federal court this week, as first reported by The Hollywood Reporter, potentially opening the door to more lawsuits involving cloud-based services.

Box.net advertises itself as a secure way for small or medium-sized businesses to share and collaborate on files. Businesses can use it as an alternative to Microsoft's SharePoint and can even hook it up with a Google Apps account for the company. In some ways, it's a lot like Dropbox—and users can use a free Box.net account for personal use if they want—but it's largely geared toward businesses.

According to the declaration filed Wednesday, however, the RIAA has already singled out several Box.net users for having copyrighted music files on their accounts, which the RIAA tells Ars were prerelease recordings. The organization is requesting that the clerk issue a subpoena to Box.net in order for the RIAA to obtain the identities of those users "who have reproduced and are offering for distribution our members' copyrighted sound recordings without their authorization."

The move seems to have taken some by surprise—after all, the RIAA has traditionally gone after P2P users and recently made a $105 million settlement with Limewire in order to put its five-year-long copyright suit behind it. It's the BitTorrents and the RapidShares of the world that typically need to fear the RIAA's wrath, not cloud-based services like Box.net. It's a legit service, unlike many of the P2P services Big Content usually targets.

The RIAA declined to give further details about what it's trying to get out of Box.net, but did say that the cloud part of the equation was not a factor. "The RIAA issued a 512(h) subpoena on Box.Net as part of a routine investigation into a pre-release leak. The fact that Box.Net is a cloud service has nothing to do with our investigation," RIAA spokesperson Cara Duckworth told Ars.

As for Box.net, the company told The Hollywood Reporter that it would comply with the court order when it comes. "Our compliance will be limited to the information the court requires we produce. At Box, we're primarily focused on powering collaboration and information sharing within businesses, and it's rare that we run into copyright infringement issues in those instances," the company said.