The NMFA has that possibility covered also:
NATIONAL MASTER
FREIGHT AGREEMENT
Article 32, Section 6
A. It is a violation of Article 32 to use vendors to perform work,
other than overflow, of the kind, nature, or type currently or previously
performed by bargaining unit employees. For example, it is a
violation of Article 32 for the size of the bargaining unit to decrease
by attrition and the Employer not replace the employees while using
vendors to perform work of the kind, nature, or type previously performed
by that bargaining unit. Bargaining unit work of the kind,
nature, or type includes any pick-up or delivery of freight, dockwork,
clerical, or maintenance work functions performed by the
bargaining unit under the Agreement.