Oh look...the Labor Day organizers have the Supreme Court on their side...
The United States Supreme Court, in a rare 9-0 decision, ruled that parades are protected under the First Amendment, and as such, the state could not compel organizers to include groups with messages the organizers disfavored. Justice Souter, writing for the Court, noted, "The state court's application [of the public accommodation law] however, had the effect of declaring the sponsor's speech itself to be the public accommodation."
"Under the free speech guarantees of the Federal Constitution's First Amendment, (1) the law is not free to interfere with speech for no better reason than promoting an approved message or discouraging a disfavored one, however enlightened either purpose may strike the government, and (2) disapproval of a private speaker's statement does not legitimize use of the government's power to compel the speaker to alter the message by including one more acceptable to others."
The Court also observed, "Assuming a parade to be large enough and to be a source of public benefits, apart from the parade's expression, that would normally justify application to the parade of a mandated access provision, a group can nonetheless, consistent with the free speech guarantee of the First Amendment, be refused admission to the parade as an expressive contingent with its own message just as readily as a private club can exclude an applicant whose manifest views are at odds with a position taken by the club's existing members."