Pardon my language, in advance

Today at a meeting I heard from a woman who works for a nonprofit serving homeless people. She informed us that she has (personally) been receiving subpoenas from the Department of Homeland Security requesting information on certain of her agency's clients, and whether the agency can assure that said clients are not on any terrorist watch lists. She was threatened with jail if she informs any of these individuals about the interest shown towards them by the nice people at Homeland Security. She assured us that the individuals in question have jobs, and families, and social security numbers, and no criminal history whatsoever.

So, now it appears I'm involved in an effort to organize a little workshop for social service providers to try to answer questions like: Under what authority are these subpoenas / requests/ threats made? What is the extent of that authority? On what basis are these requests triggered? How would, say, your run-of-the-mill homeless shelter or health clinic or food bank assess the likelihood of a visit from the subpoena-weilding Men in Black? What recourse or resources are available to these organizations and their employees?

This? This is some messed up shit, right here.