Employers and unions can bargain over permissive items if they choose, but since they are outside the boundaries of the NLRA, the NLRB cannot order bargaining on these issues.

Permissive Items

Items in collective bargaining that can be negotiated, but are not mandatory to include in agreements.

NLRB

The National Labor Relations Board, a federal agency in the United States responsible for enforcing US labor law in relation to collective bargaining and unfair labor practices.