If you are in Local 705, the NMA doesn't apply to you. But this almost identical language from Local 705's Contract does:
ARTICLE 22. PART-TIME EMPLOYEES
Section 4.
Part-time employees shall be given the opportunity to fill full-time jobs before hiring from the outside on a six-for-one basis [six (6) part-time to every one (1) outside hire].
The following shall be incorporated into the job selection procedures in this Agreement.
The Employer shall fill all vacancies and permanent new jobs for part-time employees from the part-time selection list in all months except November and December.
Part-time employees with seniority shall have the right to place their name on the list of employees waiting to be moved to a preferred job within their building. Such preferred jobs shall include, but not be limited to: Preload, Sorter, Clerical, Irregular Train, Designated Responder, Carwasher, Loader and Unloader. Employees do not have the right to select any specific unit, load or workstation unless a prior past practice has been established.
A maximum of twenty-five percent (25%) of the employees on a shift shall be allowed to change shifts in any one (1) calendar year. The employee obtaining the new position shall remain on that shift for at least six (6) months.