Congress passed the National Labor Relations Act (NLRA) in 1935 (29 U.S.C.A. No. 151 and following) to establish the right of workers to collective bargaining and other group activities. The NLRA also created the National Labor Relations Board (NLRB), a federal authority empowered to enforce the right to collective bargaining (No. 153). The NLRA has been amended several times since 1935, including 1947, 1959 and 1974. Portuguese law distinguishes three types of collective agreements according to the nature of the signatories on the employer side (Article 2, Collective Labour Relations Act): association agreements negotiated by employers` organisations; multi-employer agreements negotiated by a number of employers who, whether or not they are members of employer organizations, do not act through any association to negotiate the agreement in question; Agreements concluded at the company level by a single employer. This distinction is used by law to resolve specific conflicts between collective agreements (see also collective bargaining: level of bargaining, instruments of collective labour regulation). Another legal distinction, based on the different nature of the scope of collective agreements, is defined by horizontal and vertical agreements (see below). One area of the ongoing conflict between unions and employers is that wage increases are mandatory bargaining partners. In Acme Die Casting v.
NLRB, 26 F.3d 162 (D.C. Cir. 1994), the Court of Appeal analyzed the employer`s historical practice of determining the frequency and size of wage increases and found that the issue of granting a wage increase is not left to the employer`s discretion and cannot be decided without negotiation with the union. Since 2003, the U.S. Supreme Court has failed to resolve whether wage increases are mandatory collective bargaining issues, so federal appels courts have developed their own rules to address this issue. If an employer does not exercise discretion to determine the date or amount of the wage increase, the issue of wage increases is a matter of collective bargaining.