Opinion of the Court. 327 U.S. actually done but the entire employer-employee relationship for which compensation is paid to the employee by the employer." An argument against the interpretation which we give to "service performed" is the contrary ruling of the governmental agencies which are charged with the administration of the Social Security Act. Their competence 17 For example the Social Security Board's Regulations No. 3 in considering "wages" treats vacation allowances as wages. 26 CFR, 1940 Supp., 402.227 (b). Compare Armour & Co. v. Wantock, 323 U. S. 126, 133. Treasury Department Regulations No. 91 relating to the Employees' Tax and the Employer's Tax under Title VIII of the Social Security Act, 1936, Art. 16, classifies dismissal pay, vacation allowances or sick pay as wages. Regulations, 106 under the Federal Insurance Contributions Act, 1940, pp. 48, 51, continues to consider vacation allowances as wages. It differentiates voluntary dismissal pay, I. R. B., 1940, 1-22-10271, S. S. T. 389, an Office Decision, holds that amounts paid employees during absence on jury service to make their pay equivalent to regular salary are wages. Though formal action was taken by the Social Security Board on March 27, 1942, our attention has not been called to any regulation of any governmental agency excluding "back pay" from wages. The Treasury Department has authority to issue regulations for Social Security taxes. §§ 808 and 908, 49 Stat. 638, et seq.; I. R. C., § 1429, 53 Stat. 178. So has the Social Security Board, § 1102, 49 Stat. 647, and § 205 (a), 53 Stat. 1368. All authority for the promulgation of regulations limits the action to rules and regulations not inconsistent with the provisions of the various sections. In regulations governing the collection of income taxes at source on or after January 1, 1945, 58 Stat. 247, the Bureau of Internal Revenue classified vacation allowances and dismissal pay as wages under the following statutory definition of wages: "Sec. 1621. Definitions. As used in this subchapter (a) Wages.-The term 'wages' means all remuneration (other than fees paid to a public official) for services performed by an employee for his employer, including the cash value of all remuneration paid in any medium other than cash; except that such term shall not include remuneration paid-" See 26 CFR, 1944 Supp., 405.101 (d) and (e). 358 Opinion of the Court. 18 and experience in this field command us to reflect before we decide contrary to their conclusion. The first administrative determination was apparently made in 1939 by an Office Decision of the Bureau of Internal Revenue on the problem of whether "back pay" under a Labor Board order was wages subject to tax under Titles VIII and IX of the Social Security Act which the Bureau collects.1 The back pay was held not to be subject as wages to the tax because no service was performed, the employer had tried to terminate the employment relationship and the allowance of back pay was discretionary with the Labor Board. Reliance for the conclusions was placed upon Agwilines, Inc. v. Labor Board, 87 F. 2d 146, which had held "back pay" a public reparation order and therefore not triable by jury as a private right for wages would have been. This position is maintained by the Social Security Board by minute of March 27, 1942. It is followed by the National Labor Relations Board which at one time approved the retention by the employer of the tax on the employees' back pay for transmission to the Treasury Department as a tax on wages but later reversed its position on the authority of the Office Decision to which reference has just been made. Re Pennsylvania Furnace & Iron Co., 13 N. L. R. B. 49, 53 (5), 54, 58.19 The Office Decision seems to us unsound. The portion of the Agwilines decision, which the Office Decision relied upon, was directed at the constitutional claim to a right of trial by jury. It stated that "back pay" was not a penalty or damages which a private individual might 18 I. R. B., 1939, 1–14-9776, S. S. T. 359. No regulations covering "back pay" under the Social Security Act have been found. They are authorized by §§ 808 and 908, 49 Stat. 638, 643. 19 The States have largely followed the Bureau of Internal Revenue in their classification of "back pay." Some have disagreed. Unemployment Insurance Service, All State Treatise, C. C. H., Paragraph 1201. See Matter of Tonra, 258 App. Div. 835, 15 N. Y. S. 2d 755; 283 N. Y. 676, 28 N. E. 2d 402. Opinion of the Court. 327 U.S. claim. But there is nothing in the opinion which supports the idea that the "back pay" award differs from other pay. Indeed the opinion said that "Congress has the right to eradicate them [unfair practices] as from the beginning." 87 F. 2d at 151, 1. c. We think the true relation of awards of "back pay" to compensation appears in the Republic Steel and Phelps-Dodge cases, hereinbefore discussed.20 But it is urged by petitioner that the administrative construction on the question of whether "back pay" is to be treated as wages should lead us to follow the agencies' determination. There is a suggestion that the administrative decision should be treated as conclusive, and reliance for that argument is placed upon Labor Board v. Hearst Publications, 322 U. S. 111, 130, and Gray v. Powell, 314 U. S. 402, 411. In the acts which were construed in the cases just cited, as in the Social Security Act, the administrators of those acts were given power to reach preliminary conclusions as to coverage in the application of the respective acts. Each act contains a standardized phrase that Board findings supported by substantial evidence shall be conclusive." The validity of regulations is specifically reserved for judicial determination by the Social Security Act Amendments of 1939, § 205 (g). The Social Security Board and the Treasury were compelled to decide, administratively, whether or not to treat "back pay" as wages; and their expert judgment is entitled, as we have said, to great weight.22 The very fact 20 This was the view of the Eighth Circuit when a "back pay" claim was presented in bankruptcy. Labor Board v. Killoren, 122 F. 2d 609, 614. 21 National Labor Relations Act, 49 Stat. 454, § 10 (e); Bituminous Coal Act of 1937, 50 Stat. 72, 85, § 4-A; Social Security Act Amendments of 1939, § 205 (c) (3) and (g). 22 See Sanford v. Commissioner, 308 U. S. 39, 52; Skidmore v. Swift & Co., 323 U. S. 134, 139–40. 358 Opinion of the Court. that judicial review has been accorded, however, makes evident that such decisions are only conclusive as to properly supported findings of fact. Both Hearst Publications, p. 131, and Gray v. Powell, p. 411, advert to the limitations of administrative interpretations. Administrative determinations must have a basis in law and must be within the granted authority. Administration, when it interprets a statute so as to make it apply to particular circumstances, acts as a delegate to the legislative power. Congress might have declared that "back pay" awards under the Labor Act should or should not be treated as wages. Congress might have delegated to the Social Security Board to determine what compensation paid by employers to employees should be treated as wages. Except as such interpretive power may be included in the agencies' administrative functions, Congress did neither. An agency may not finally decide the limits of its statutory power. That is a judicial function.23 Congress used a well understood word-"wages"to indicate the receipts which were to govern taxes and benefits under the Social Security Act. There may be borderline payments to employees on which courts would follow administrative determination as to whether such payments were or were not wages under the act. We conclude, however, that the Board's interpretation of this statute to exclude back pay goes beyond the boundaries of administrative routine and the statutory limits. This is a ruling which excludes from the ambit 23 American School of Magnetic Healing v. McAnnulty, 187 U. S. 94, 110; International R. Co. v. Davidson, 257 U. S. 506, 514; Iselin v. United States, 270 U. S. 245; Koshland v. Helvering, 298 U. S. 441; Federal Communications Comm'n v. Pottsville Broadcasting Co., 309 U. S. 134, 144-145; United States v. Carolina Carriers Corp., 315 U. S. 475, 489; Helvering v. Credit Alliance Co., 316 U. S. 107, 113; Helvering v. Sabine Transportation Co., 318 U. S. 306, 311-12; Addison v. Holly Hill Co., 322 U. S. 607, 611, et seq.; cf. Steuart & Bro. v. Bowles, 322 U. S. 398, 403. FRANKFURTER, J., concurring. 327 U.S. of the Social Security Act payments which we think were included by Congress. It is beyond the permissible limits of administrative interpretation. Petitioner further questions the validity of the decision of the circuit court of appeals on the ground that it must be inferred from the opinion that the "back pay" must be allocated as wages by the Board to the "calendar quarters" of the year in which the money would have been earned, if the employee had not been wrongfully discharged. We think this inference is correct." This conclusion, petitioner argues, tends to show that "back pay" cannot be wages because the Amendments of 1939 use "quarters" as the basis for eligibility as well as the measure of benefits and require "wages" to be "paid" in certain "quarters." 25 If, as we have held above, "back pay" is to be treated as wages, we have no doubt that it should be allocated to the periods when the regular wages were not paid as usual. Admittedly there are accounting difficulties which the Board will be called upon to solve but we do not believe they are insuperable." Affirmed. MR. JUSTICE JACKSON took no part in the consideration or decision of this case. MR. JUSTICE FRANKFURTER, concurring. The decisions of this Court leave no doubt that a man's time may, as a matter of law, be in the service of another 24 See Nierotko v. Social Security Board, 149 F. 2d 273, 274, r. c. 25 See note 7, supra. The same problem would arise under the Social Security Act, 49 Stat. 625, § 210 (c). 28 The Social Security Board itself has recommended the inclusion of "back pay" in wages. Annual Report of the Federal Security Agency, Social Security Board (1945), § 5, p. 398: "Certain items of income which are now not considered 'wages' under the definition in the act, should be included as wages, so that the |