[unclebucknasty]

The question is, what law(s) are being used by the government to take these actions with Twitter/Yahoo? For instance, are these NSL letters?

If these are not actual laws, but rather gray-area interpretations of laws being used, then each company can decide whether to challenge them and have their days in court.

But, if the government is clearly operating within the law, then it is the law/lawmaking itself that should be challenged.