"But while labels like “terrorist” and “criminal” are conceptually broad, they look more like narrow racial and religious proxies once you see how they are applied to people and groups in the list, experts said, raising the likelihood that Facebook is placing discriminatory limitations on speech."

Terrorist organizations according to Facebook include the Iran Tractor Manufacturing Company.

Given that it was sanctioned by the US government for being a terrorist funding source, it's not exactly surprising that a US company has rules against them. That's a category they can't do much except ban them.

American companies are required to comply with restrictions on the SDN list maintained by the treasury department.

larger discussion ended up here: https://news.ycombinator.com/item?id=28843122