delivered the opinion of the Court.
The question presented by this case is whether foremen are entitled as a class to the rights of self-organization, collective bargaining, and other concerted activities as assured to employees generally by the National Labor Relations Act. The case grows out of conditions in the automotive industry, and so far as they are important to the legal issues here the facts are simple.
*487The Packard Motor Car Company employs about 32,000 rank-and-file workmen. Since 1937 they have been represented by the United Automobile Workers of America affiliated with the Congress of Industrial Organizations. These employees are supervised by approximately 1,100 employees of foreman rank, consisting of about 125 “general foremen,” 643 “foremen,” 273 “assistant foremen,” and 65 “special assignment men.” Each general foreman is in charge of one or more departments, and under him in authority are foremen and their assistant foremen. Special assignment men are described as “troubleshooters.”
The function of these foremen in generalas typical of the duties of foremen in mass-production industry generally. Foremen carry the responsibility for maintaining quantity and quality of production, subject, of course, to the overall control and supervision of the management. Hiring is done by the labor relations department, as is the discharging and laying off of employees. But the foremen are provided with forms and with detailed lists of penalties to be applied in cases of violations of discipline, and initiate recommendations for promotion, demotion and discipline. All such recommendations are subject to the reviewing procedure concerning grievances provided in the collectively-bargained agreement between the Company and the rank-and-file union.
The foremen as a group are highly paid and, unlike the workmen, are paid for justifiable absence and for holidays, are not docked in pay when tardy, receive longer paid vacations, and are given severance pay upon release by the Company.
These foremen determined to organize as a unit of the Foremen’s Association of America, an unaffiliated organization which represents supervisory employees exclusively. Following the usual procedure, after the Board had decided that “all general foremen, foremen, assistant fore*488men, and special assignment men employed by the Company at its plants in Detroit, Michigan, constitute a unit appropriate for the purposes of collective bargaining within the meaning of Section 9 (b) of the Act,”1 the Foremen’s Association was certified as the bargaining representative. The Company asserted that foremen were not “employees” entitled to the advantages of the Labor Act, and refused to bargain with the union. After hearing on charge of unfair labor practice, the Board issued the usual cease-and-desist order. The Company resisted and challenged validity of the order. The judgment of the court below decreed its enforcement, 157 F. 2d 80, and we granted certiorari. 329 U. S. 707.
The issue of law as to the power of the National Labor Relations Board under the National Labor Relations Act is simple and our only function is to determine whether the order of the Board is authorized by the statute.
The privileges and benefits of the Act are conferred upon employees, and § 2 (3) of the Act, so far as relevant, provides “The term 'employee’ shall include any employee . . . .” 49 Stat. 450. The point that these foremen are employees both in the most technical sense at common law as well as in common acceptance of the term, is too obvious to be labored. The Company, however, turns to the Act’s definition of employer, which it contends reads foremen out of the employee class and into the class of employers. Section 2 (2) reads: “The term 'employer’ includes any person acting in the interest of an employer, directly or indirectly . . . .” 49 Stat. 450. The context of the Act, we think, leaves no room for a construction of this section to deny the organizational privilege to employees because they act in the interest of an employer. Every employee, from the very fact of employment in the master’s business, is required to act in his interest. He *489owes to the employer faithful performance of service in his interest, the protection of the employer’s property in his custody or control, and all employees may, as to third parties, act in the interests of the employer to such an extent that he is liable for their wrongful acts. A familiar example would be that of a truck driver for whose negligence the Company might have to answer.
The purpose of § 2 (2) seems obviously to render employers responsible in labor practices for acts of any persons performed in their interests. It is an adaptation of the ancient maxim of the common law, respondeat superior, by which a principal is made liable for the tortious acts of his agent and the master for the wrongful acts of his servants. Even without special statutory provision, the rule would apply to many relations. But Congress was creating a new class of wrongful acts to be known as unfair labor practices, and it could not be certain that the courts would apply the tort rule of respondeat superior to those derelictions. Even if it did, the problem of proof as applied to this kind of wrongs might easily be complicated by questions as to the scope of the actor’s authority and of variance between his apparent and his real authority. Hence, it was provided that in administering this act the employer, for its purposes, should be not merely the individual or corporation which was the employing entity, but also others, whether employee or not, who are “acting in the,interest of an employer.”
Even those who act for the employer in some matters, including the service of standing between management and manual labor, still have interests of their own as employees. Though the foreman is the faithful representative of the employer in maintaining a production schedule, his interest properly may be adverse to that of the employer when it comes to fixing his own wages, hours, seniority rights or working conditions. He does not lose his right to serve himself in these respects because he *490serves his master in others. And we see no basis in this Act whatever for holding that foremen are forbidden the protection of the Act when they take collective action to protect their collective interests.
The company’s argument is really addressed to the undesirability of permitting foremen to organize. It wants selfless representatives of its interest. It fears that if foremen combine to bargain advantages for themselves, they will sometimes be governed by interests of their own or of their fellow foremen, rather than by the company’s interest. There is nothing new in this argument. It is rooted in the misconception that because the employer has the right to wholehearted loyalty in the performance of the contract of employment, the employee does not have the right to protect his independent and adverse interest in the terms of the contract itself and the conditions of work. But the effect of the National Labor Relations Act is otherwise, and it is for Congress, not for us, to create exceptions or qualifications at odds with its plain terms.
Moreover, the company concedes that foremen have a right to organize. What it denies is that the statute compels it to recognize the union. In other words, it wants to be free to fight the foremen’s union in the way that companies fought other unions before the Labor Act. But there is nothing in the Act which indicates that Congress intended to deny its benefits to foremen as employees, if they choose to believe that their interests as employees would be better served by organization than by individual competition.2 N. L. R. B. v. Skinner & Kennedy Stationery Co., 113 F. 2d 667; see N. L. R. B. v. Armour & Co., 154 F. 2d 570, 574.
*491There is no more reason to conclude that the law prohibits foremen as a class from constituting an appropriate bargaining unit than there is for concluding that they are not within the Act at all. Section 9(b) of the Act confers upon the Board a broad discretion to determine appropriate units. It reads, “The Board shall decide in each case whether, in order to insure to employees the full benefit of their right to self-organization and to collective bargaining, and otherwise to effectuate the policies of this Act, the unit appropriate for the purposes of collective bargaining shall be the employer unit, craft unit, plant unit, or subdivision thereof.” 49 Stat. 453. Our power of review also is circumscribed by the provision that findings of the Board as to the facts, if supported by evidence, shall be conclusive. § 10 (e), 49 Stat. 454. So we have power only to determine whether there is substantial evidence to support the Board, or its order oversteps the law. N. L. R. B. v. Link-Belt Co., 311 U. S. 584; Pittsburgh Plate Glass Co. v. N. L. R. B., 313 U. S. 146.
There is clearly substantial evidence in support of the determination that foremen are an appropriate unit by themselves and there is equal evidence that, while the foremen included in this unit have different degrees of responsibility and work at different levels of authority, they have such a common relationship to the enterprise and to other levels of workmen that inclusion of all such grades of foremen in a single unit is appropriate. Hence the order insofar as it depends on facts is beyond our power of review. The issue as to what unit is appropriate for bargaining is one for which no absolute rule of law is laid down by statute, and none should be by decision. It involves of necessity a large measure of informed discretion, and the decision of the Board, if not final, is rarely to be disturbed. While we do not say that a determination of a unit of representation cannot be so unreasonable and arbitrary as to exceed the Board’s power, we are clear that *492the decision in question does not do so. That settled, our power is at an end.
We are invited to make a lengthy examination of views expressed in Congress while this and later legislation was pending to show that exclusion of foremen was intended. There is, however, no ambiguity in this Act to be clarified by resort to legislative history, either of the Act itself or of subsequent legislative proposals which failed to become law.
Counsel also would persuade us to make a contrary interpretation by citing a long record of inaction, vacillation and division of the National Labor Relations Board in applying this Act to foremen. If we were obliged to depend upon administrative interpretation for light in finding the meaning of the statute, the inconsistency of the Board’s decisions would leave us in the dark.3 But there are difficult questions of policy involved in these cases which, together with changes in Board membership, account for the contradictory views that characterize their history in the Board. Whatever special questions there are in determining the appropriate bargaining unit for *493foremen are for the Board, and the history of the issue in the Board shows the difficulty of the problem committed to its discretion. We are not at liberty to be governed by those policy considerations in deciding the naked question of law whether the Board is now, in this case, acting within the terms of the statute.
It is also urged upon us most seriously that unionization of foremen is from many points bad industrial policy, that it puts the union foreman in the position of serving two masters, divides his loyalty and makes generally for bad relations between management and labor. However we might appraise the force of these arguments as a policy matter, we are not authorized to base decision of a question of law upon them. They concern the wisdom of the legislation; they cannot alter the meaning of otherwise plain provisions.
The judgment of enforcement is
Affirmed.
61 N. L. R. B. 4, 26.
If a union of vice presidents, presidents or others of like relationship to a corporation comes here claiming rights under this Act, it will be time enough then to point out the obvious and relevant differences between the 1,100 foremen of this company and corporate officers elected by the board of directors.
The Board had held that supervisory employees may organize in an independent union, Union Collieries Coal Co., 41 N. L. R. B. 961, 44 N. L. R. B. 165; and in an affiliated union, Godchaux Sugars, Inc., 44 N. L. R. B. 874. Then it held that there was no unit appropriate to the organization of supervisory employees. Maryland Drydock Co., 49 N. L. R. B. 733; Boeing Aircraft Co., 51 N. L. R. B. 67; Murray Corp. of America, 51 N. L. R. B. 94; General Motors Corp., 51 N. L. R. B. 457. In this case, 61 N. L. R. B. 4, 64 N. L. R. B. 1212; in L. A. Young Spring & Wire Corp., 65 N. L. R. B. 298; Jones & Laughlin Steel Corp., 66 N. L. R. B. 386, 71 N. L. R. B. 1261; and in California Packing Corp., 66 N. L. R. B. 1461, the Board re-embraced its earlier conclusions with the same progressive boldness it had shown in the Union Collieries and Godchaux Sugars cases. In none of this series of cases did the Board hold that supervisors were not employees. See Soss Manufacturing Co., 56 N. L. R. B. 348.