Imagine you're a human rights activist working for an NGO in Sri Lanka.  After a hard day's work in a humid office building, you walk into your apartment, fire up your laptop and fire off the following tweet:

"Holding workshop with @LTTE and Sri Lankan govt. about easing roadblocks for medical supplies to be trucked in.  Conf. going well, God-willing."

Congratulations, you're now a terrorist.

It sounds like the plot of an action movie.  But according to a controversial 2010 ruling by the U.S. Supreme Court, NGOs--and those who work on their behalf--could be held criminally and civilly liable for providing nonviolent, material support to designated terrorist groups.

In Holder v. Humanitarian Law Project, the Court extended the Patriot Act's prohibition on material support to terrorist groups to include "expert advice, assistance, and personnel".  Under the contentious 6-3 decision, aiding and abetting the enemy could be as innocent as providing antibiotics to refugees ...or as amorphous as sending out a tweet.

The decision already has its share of detractors.  Former President Jimmy Carter and linguist Noam Chomsky have already come out against it, warning that the decision could hamper the work of NGOs around the world and endanger the lives of civilians in war-torn areas, including women and children.  But is promoting social justice in Sri Lanka the same as shouting fire in a crowded theater?

Yes, says Nitsana Darshan-Leiter.

Leiter, who is Israeli, seems like an unlikely proponent for the new ruling.  But already her group, Shurat Haddin, is using the Holder decision to sue social media giants such as Twitter, accusing them of violating U.S. anti-terror laws by hosting the accounts of Hezbollah, al-Shabaab, and other terrorist groups .  In a recent interview with the Jerusalem Post, Darshan-Leiter claims that unless the accounts are deleted, the California-based tech company could face fines, even indictments.

But who determines who is and isn't a terrorist?

According to the Supreme Court, that task falls to Congress and the Executive Branch.  But even then, the issue is murky.  The State Department has designated the MEK, or Mujaheddin al Khalq, as a terrorist group for its involvement in the 1980-88 Iran-Iraq war.  Yet according to the International Herald Tribune, politicians as diverse as Patrick Kennedy and former Homeland Security chief Tom Ridge have endorsed the group, as well as former chief of staff Andrew Card, Richard Perle, and many others.

Kennedy, a Democrat, even voted for a non-binding resolution endorsing the group.  Yet organizations like Hezbollah--which has a social service wing as well--are conspicuously excluded.

As the global war on terror continues, the only sure advice seems to be: watch what you tweet.

By John Winn