I think that would have to be under federal law, and I don't think federal law precludes the good professor from this sort of activism.
I don't think smoking is a substantive "right, privilege, or immunity" from the federal Constiutional law standpoint. Under the Slaughterhouse cases from the 1880's, which are still good law, the only federal privileges and immunities that exist are those integral to national citizenship, e.g. the right to vote in a Congressional election, the right to travel unhindered to the District of Columbia, etc.
Wisconsin law, acc. to this article, forbids Prof Munson (a state employee) from using his position for political advocacy. Since Mad Munson was urging his students to support the anti-smoking referendum, he broke that law.