Riot Games is one of these studios that have piped up to oppose the bill, as CEO Brandon Beck posted a lengthy reasoning as to why SOPA would harm League of Legends specifically, and he asked players to help stop it from being passed into law. "While we do support efforts to prevent online piracy, the current form of this legislation comes at far too high a cost for us, our players, and online communities across the internet," Beck writes, citing examples as to how the game could be taken offline and the community dismantled if the SOPA were wielded against LoL.
Interestingly enough, Colorado Rep. Jared Polis, who is himself a League of Legends player, replied to Beck in support of Riot Games' stance: "I'm particularly concerned that SOPA might stifle the kind of innovation that brings us games we love, such as LoL. The bill makes it far too easy for angry competitors to sue good law abiding companies out of existence." Polis says that he is drafting an alternate piece of legislation to combat internet piracy without SOPA's potential abuse.
[Update: If you'd like to encourage other companies to blockade SOPA, you might be interested in the online petition aimed squarely at Electronic Arts.]