Yesterday the Supreme Court upheld the material support law. This was an add-on to the patriots act making it illegal to provide material support to any foreign terrorist group that's on the US list.
There is a huge amount of wiggle room in the current law as the definitions of terrorist groups and material support are very loose.
The ruling came in a lawsuit filed on behalf of the Humanitarian Law Project. The group provides nonviolent dispute resolution and human rights advocacy training to the Kurdistan Workers’ Party and several groups of Tamil Americans who sought to provide humanitarian relief in war-torn areas of Sri Lanka once controlled by the Tamil Tigers. The non-profit org has not been charged with a crime.
It's a bit of a slippery slope argument at this point. I don't think the US has gone after any humanitarian peace-making orgs, but it seems like civil rights have been hacked away. Reportedly, journalists are fearful of even writing op-ed pieces about anyone on the 'list'.