The United States Supreme Court held that while the National Labor Relations Board does have power under the Labor Management Relations Act to require employers and employees to negotiate, it is without power to compel a company or a union to agree to any substantive contractual provision of a collective bargaining agreement.
H. K. Porter Co. v. NLRB, 397 U. S. 99 (1970).
J. P. Kelly,
Labor Law - NLRB's Remedial Powers,
Duq. L. Rev.
Available at: https://dsc.duq.edu/dlr/vol9/iss3/14