The measure would also outlaw surreptitious videotaping of movies in theaters.
According to the sponsoring senators the bill targets practices that over the past several years have disrupted release schedules and cost movie makers an estimated $3 billion annually in lost sales.
Unauthorized copies of movies often turn up in flea markets and online "peer to peer" networks such as Kazaa shortly after they are released, thanks to audience members who smuggle camcorders into theaters.
In other cases, industry insiders post movies online before they are officially released.
Both practices would become felonies under the bill, with maximum sentences of five years for first offenders as well as monetary damages.
Copyright infringement is already illegal, but the bill would make such activity easier to prosecute by assuming that any copyrighted work posted online ahead of its release date has been downloaded at least 10 times, causing damages of at least $2,500.
Lobbyists from the movie and recording industries applauded the bill.