The collective bargaining agreement between American University and SEIU Local 500 provides that, except those covered by an exemption, all faculty members who become employed by the University and covered by the Agreement must either voluntarily become members of the Union, or shall be required as a condition of continued employment to pay to the Union each month a service charge as a contribution toward the cost of administration of the Agreement and representation by the Union, beginning no later than thirty-one (31) days after the date of their initial appointment.