The subpoena demands the name of the user who uploaded the first episode of the new season of 24 before it was aired on TV and 12 episodes of The Simpsons. It was filed on 18 January in the US District Court for the Northern District of California.
The clips were posted by a subscriber identified as ECOtotal and it is suspected that they either work in the studio or are a member of the press who received preview copies of the shows.
Video site LiveDigital was also found to have the same material uploaded by a user called Jorge Romero, and has been included in the subpoena.
The material has now been taken down from both sites.
20th Century Fox has already had privacy issues involving Google-owned YouTube when a user was identified in a case in which a Family Guyepisode was posted ahead of its premiere.
The issue has sparked concern among entertainment companies and there is a debate about whether video-sharing sites should be financially accountable.
Meanwhile, YouTube has said it will start to share revenues with amateur videographers in a bid to increase the level of creativity on the site.
Speaking at the World Economic Forum at Davos, YouTube co-founder Chad Hurley said: 'We are getting an audience large enough where we have an opportunity to support creativity, to foster creativity through sharing revenue with our users. So in the coming months we are going to be opening that up.'