Here’s the AJS’s explanation, from its web site, for why — apart from the fact that they don’t have to— they don’t name their “members” (note, it’s partly the “media’s” fault):

Our members are businesses, business leaders and entrepreneurs from around the country. AJS does not disclose or discuss its membership further than this. Too often politicians or the media define an organization or message not by the merits of the argument, but rather by the perception of the people associated with it. We would rather the people decide on merits instead of name-calling.

While the public may not know who Americans for Job Security’s “members” are, many people have or will experience their “membership dues” in action. Reports McIntire:

This week, emboldened by the court ruling, the group paid close to $4 million…for ads directly attacking nine Democratic candidates for Congress. That made it among the first to abandon the old approach of running ads that stopped just short of explicitly urging voters to elect or reject individual candidates.

This morning, PolitiFact gave a “half-true” rating to one such ad.

Liz Cox Barrett is a writer at CJR.