The Supreme Court has sustained First Amendment challenges to allegedly compelled expression in two categories of cases: true 'compelled-speech' cases, in which an individual is obliged personally to express a message he disagrees with, imposed by the government; and 'compelled-subsidy' cases, in which an individual is required by the government to subsidize a message he disagrees with, expressed by a private entity. See First Amendment (commercial speech: compelling views) for the latter.
The court first invalidated an outright compulsion of speech in West Virginia Bd. of Ed. v. Barnette, 319 U. S. 624 (1943). The State required every schoolchild to recite the Pledge of Allegiance while saluting the American flag, on pain of expulsion from the public schools. We held that the First Amendment does not 'le[ave] it open to public authorities to compel [a person] to utter' a message with which he does not agree. Id., at 634. Likewise, in Wooley v. Maynard, 430 U. S. 705 (1977), it held that requiring a New Hampshire couple to bear the State's motto, 'Live Free or Die,' on their cars' license plates was an impermissible compulsion of expression. Obliging people to 'use their private property ...