SOPA and its counterpart in the US-Senate, PROTECT IP would he government to obtain blocking orders without an adversary proceeding against Web sites with copyright infringements. The order may target internet access providers, search engines, DNS providers, advertisers and others. SOPA will address non-US providers too.
In addition, SOPA allowing injunctions against tools that could be used to circumvent the blocking orders. At first Firefox add-ons like MAFIAAFire, ThePirateBay Dancing or DeSOPA became illegal. The U.S. Department of Homeland Security has already tried to remove MAFIAAFire from the Web (unsuccessfully so far).
But the anti-circumvention part of SOPA is not limited to Firefox add-ons. It targets anyone who:
knowingly and willfully provides or offers to provide a product or service designed or marketed by such entity...for the circumvention or bypassing of a Justice Department-erected blockade.
With this law the using of JonDonym and marketing for JonDonym may became illegal. But not only JonDonym is affected by this law. VPNs can also "bypass" a SOPA-established blockade and TorProject.org, which is funded in part by multiple federal US-agencies, is promoted for circumvent internet censorship too. Because Tor is widely used by US intelligence services and military it doesn't be a target for injunctions. But the law is not clear. It depends on the US government to use the law to prohibit a service or not.
More information about SOPA were published by EFF.org