The University of Wisconsin requires all of its students to pay, as part of their tuition, a student activity fee. Those fees are used to support campus clubs and activities. Some students who objected to the philosophies and activities of some of the student clubs filed suit to have the fees halted. What constitutional basis do you think they could use for the suit? [Board of Regents of Wisconsin System v. Southworth, 529 U.S. 217]