Positions outside the Bargaining Unit (a) An employee may substitute temporarily in a position outside the bargaining unit for up to fifteen (15) months from the date of the assignment. Bargaining unit employees shall be given the first opportunity to fill the resulting vacancy. The employee shall have the right to return to her or his bargaining unit position prior to the expiry of the fifteen (15) month period by giving the Employer six (6) weeks’ notice. Where an employee is backfilling outside of the bargaining unit for purposes of pregnancy and/or parental leave, the period of time will be extended up to nineteen (19) months from the date of the assignment. An employee who remains outside of the bargaining unit beyond the period covered by this article shall lose all seniority. When the employee returns to the bargaining unit, all other employee(s) shall revert to their previous positions. An employee must remain in the bargaining unit for a period of at least three (3) months before transferring out of the bargaining unit again or she or he will lose all seniority held at the time of the subsequent transfer unless the parties agree otherwise. (b) An employee who accepts a transfer under (a) above will not be required to pay Union dues for any complete calendar month during which no bargaining unit work is performed. (c) An employee who accepts a permanent position outside of the bargaining unit will lose all seniority held at the time of the transfer. (d) The Employer will advise the Union of the names of any employees pursuant to Article 9.17(a) or (b).