After accusing YouTube of rampant copyright infringement, media giant Viacom has found an unusual ally in a fight over its own use of copyrighted material.

The Electronic Frontier Foundation (EFF) has filed an amicus brief in support of Viacom over a parody of a popular online video called "What What (In the Butt)."

Comedy Central's popular show South Park parodied the video in a 2008 episode. Two years later, copyright owner Brownmark Films sued Viacom and Comedy Central, alleging copyright infringement.

A federal judge held the parody was protected by fair use laws and dismissed the case. But Brownmark appealed to the 7th U.S Circuit Court of Appeals, claiming that fair use cannot be decided on a motion to dismiss.

The EFF says if Brownback's claim is upheld, it would have a "chilling effect" on free speech.

"Brownmark is asking the appeals court for a rule that would make it much more difficult to resolve easy fair uses cases quickly. That would discourage artists and others from fighting claims, no matter how baseless, or even engaging in the fair use in the first place," said EFF Fellow Michael Barclay. "The judge in this case got it exactly right: when the fair use is obvious, the case should be decided right away."

The EFF argued that dismissing obvious fair use cases helps to deter abuses of the copyright system by so-called "copyright trolls," who threaten to sue over copyright infringement but push to settle out of court.

"Fair use – using some copyrighted material for the purposes of art, education, or commentary – is an important part of how we communicate today. We see it everyday in segments on The Daily Show, in political advertisements, and in 'remix' videos on YouTube," said EFF Staff Attorney Julie Samuels. "We can't let litigious copyright holders chill free speech by making it more expensive."