More on US ISP termination of Iranian accounts

Slashdot linked a story by the BBC reporting that the U.S. hosting service The Planet terminated the contract of the Iranian Student News Agency (ISNA).

According to the article, ISNA is "semi-official" and may have some connections to the Iranian government. (If I recall correctly, the fundamentalist revolution in Iran called itself a "student" revolution, which may have some connection to the name of the organization.) Assuming so, the policy concerns, from the perspective of the United States, are different from a termination of a more liberal website.

There may be no effective way for a U.S. ISP to distinguish between the two kinds of websites, though, nor is it at all clear that the U.S. government should systematically engage in content-based discrimination between them. From a practical standpoint, ISP operators can't read Farsi and are unfamilar with the culture and politics of Iran, and can't be expected to make those calls anyway. It's not surprising that some ISPs are taking a bright-line approach and terminating accounts of Iranian entities and Iranians not resident in the United States, even if it silences some voices that the United States would probably like to amplify.

Assume an Iranian national resided legally in the U.S. and used a webpage hosted in the United States to write in favor of the existing Iranian government. Can the ISP terminate the contract because he is an Iranian national? Can the government require the ISP to do so without running afoul of the First Amendment? What if the Iranian national moves back to Iran?