delivered the opinion of the Court.
We are confronted here with the problem of determining, in part what constitutes work or employment in under*592ground iron ore mines within the meaning of the Fair Labor Standards Act, 52 Stat. 1060, 29 U. S. C. § 201. This question, which is one of first impression, arises out of conflicting claims based upon the actual activities pursued and upon prior custom and contract in the iron ore mines. Such an issue can be resolved only by discarding formalities and adopting a realistic attitude, recognizing that we are dealing with human beings and with a statute that is intended to secure to them the fruits of their toil and exertion.
Three iron ore mining companies, petitioners herein, filed declaratory judgment actions1 to determine whether time spent by iron ore miners in traveling underground in mines to and from the “working face”2 constitutes work or employment for which compensation must be paid under the Act. The respondent labor unions and their officials, representing petitioners’ employees, were named as defendants and the Administrator of the Wage and Hour Division of the Department of Labor was allowed to intervene. The actual controversy relates only to the hours of employment during the period intervening between the effective date of the Act, October 24,1938, and the dates when' the respective actions were initiated in April, 1941.3 It is *593conceded that if underground travel constitutes employment, the miners worked more than the statutory maximum workweek and are entitled to be paid one and one-half times the regular rate for the excess hours. But if the travel time is excluded from the workweek, thus limiting it to the time spent at the working face, no overtime payments are due.
After extended hearings, the District Court found that the travel time “bears in a substantial degree every indicia of worktime: supervision by the employer, physical and mental exertion, activity necessary to be performed for the employers’ benefit, and conditions peculiar to the occupation of mining.” The court accordingly ruled that the travel time, as well as the time spent at the surface obtaining and returning tools, lamps and carbide and checking in and out, was included within the workweek. 40 F. Supp. 4. The Circuit Court of Appeals affirmed as to the travel time, holding that the District Court’s findings on that matter were supported by substantial evidence. The judgment was modified by the Circuit Court, however, by excluding from the workweek the time spent in the activities at the surface. 135 F. 2d 320; rehearing denied, 137 F. 2d 176. The importance of the problem as to the travel time led us to grant certiorari.4
Specifically we are called upon to decide whether the District Court and the Circuit Court of Appeals properly found that iron ore miners were at work within the meaning of the Act while engaged in underground travel which they were obliged to perform on the property of and under the direction of petitioners as a necessary concomitant of their employment. The record shows that petitioners own and operate twelve underground iron ore *594mines in Jefferson County, Alabama,5 and that the general pattern of facts underlying the findings of the courts below is essentially the same in each of these mines.6
The miners begin their day by arriving on the company property at a scheduled hour7 and going to the bath house, where they change into working clothes.8 They then walk to the tally house near the mine entrance or portal; there they check in and hang up individual brass checks, furnished by petitioners, on a tally or check-in board. This enables the foreman and other officials to tell at a glance those individuals who have reported for work and those production and service crews that are incomplete and in need of substitutes. Vacancies are filled and the head miners and crews receive any necessary instructions. In addition, each miner either rents a battery lamp for the day or buys a can of carbide each day or two for underground illumination purposes. And at some of the mines, *595many miners stop at a tool box or tool house on the surface to pick up other small supplies and tools necessary for their work. These activities consume but a few minutes.
The miners thereupon are required to report at the loading platform at the mine portal and await their turn to ride down the inclined shafts of the mines. Originally the miners could reach the working faces entirely by foot, but as the shafts increased in length petitioners provided transportation down the main shafts. The miners accordingly ride part of the way to the working faces in ore skips9 or regular man trips,10 which operate on narrow gauge tracks by means of cables or hoisting ropes. The operation of the skips and man trips is under the strict control and supervision of the petitioners at all times and they refuse to permit the miners to walk rather than ride. Regular schedules are fixed; loading and unloading are supervised; the speed of the trips is regulated; and the conduct of the miners during the rides is prescribed.
About three to six trips are made, depending on the size of the mine and the number of miners. Ten men. sit on each man trip car, while from 30 to 40 are crowded into an ore skip. They are forced to jump several feet into the skip from the loading platform, which not infrequently causes injuries to ankles, feet and hands. The skips are usually overcrowded and the men stand tightly pressed together. The heads of most of them are a foot or more *596above the top of the skips. But since the skips usually clear the low mine ceilings by only a few inches, the miners are compelled to bend over. They thus ride in a close “spoon-fashion,” with bodies contorted aiid heads drawn below the level of the skip top. Broken ribs, injured arms and legs, and bloody heads often result; even fatalities are not unknown.
The length of the rides in the dark, moist, malodorous shafts varies in the different mines from 3,000 feet to 12,000 feet. The miners then climb out of the skips and man trips at the underground man-loading platforms or “hoodlums” and continue their journeys on foot for distances up to two miles. These subterranean walks are filled with discomforts and hidden perils. The surroundings are dark and dank. The air is increasingly warm and humid, the ventilation poor. Odors of human sewage, resulting from a complete absence of sanitary facilities, permeate the atmosphere. Rotting mine timbers add to the befouling of the air. Many of the passages are level, but others take the form of tunnels and steep grades. Water, muck and stray pieces of ore often make the footing uncertain. Low ceilings must be ducked and moving ore skips must be avoided. Overhead, a maze of water and air pipe lines, telephone wires, and exposed high voltage electric cables and wires present ever-dangerous obstacles, especially to those transporting tools. At all times the miners are subject to the hazards of falling rocks.
Moreover, most of the working equipment, except drills and heavy supplies, is kept near the “hoodlums.” This equipment is carried each day by foot by the crews through these perilous paths from the “hoodlums” to the working faces. Included are such items as fifty-pound sacks of dynamite, dynamite caps, fuses, gallon cans of oil and servicemen's supplies. Actual drilling and loading of the ore begin on arrival at the working faces, interrupted only by a thirty minute lunch period spent at or near the faces. *597The service and maintenance men, of course, work where-ever they are needed.
At the end of the day’s duties at the working faces, the miners lay down their drills, pick up their other equipment and retrace their steps back to the “hoodlums.” They wait there until an ore skip or man trip is available to transport them back to the portal. After arriving on the surface, they return their small tools and lamps, pick up their brass checks at the tally house, and proceed to bathe and change their clothes at the bath house. Finally they leave petitioners’ property and return to their homes.
In determining whether this underground travel constitutes compensable work or employment within the meaning of the Fair Labor Standards Act, we are not guided by any precise statutory definition of work or employment. Section 7 (a) merely provides that no one, who is engaged in commerce or in the production of goods for commerce, shall be employed for a workweek longer than the prescribed hours unless compensation is paid for the excess hours at a rate not less than one and one-half times the regular rate. Section 3 (g) defines the word “employ” to include “to suffer or permit .to work,” while § 3 (j) states that “production” includes “any process or occupation necessary to . . . production.”
But these provisions, like the other portions of the Fair Labor Standards Act, are remedial and humanitarian in purpose. We are not here dealing with mere chattels or articles of trade but with the rights of those who toil, of those who sacrifice a full measure of their freedom and talents to the- use and profit of others. Those are the rights that Congress has specially legislated to protect. Such a statute must not be interpreted or applied in a narrow, grudging manner. Accordingly we .view §§ 7 (a), 3 (g) and 3 (j) of the Act as necessarily.indicative of a Congressional intention to guarantee either , regular or overtime compensation for all actual work or employ*598ment. To hold that an employer may validly compensate his employees for only a fraction of the time consumed in actual labor would be inconsistent with the very purpose and structure of those sections of the Act. It is vital, of course, to determine first the extent of the actual workweek. Only after this is done can the minimum wage and maximum hour requirements of the Act be effectively applied. And, in the absence of a contrary legislative expression, we cannot assume that Congress here was referring to work or employment other than as those words are commonly used—as meaning physical or mental exertion (whether burdensome or not) controlled or required by the employer and pursued necessarily and primarily for the benefit of the employer and his business.11
Viewing the facts of this case as found by both courts below in the light of the foregoing considerations, we are unwilling to conclude that the underground travel in petitioners’ iron ore mines cannot be construed as work or employment within the meaning of the Act. The exacting and dangerous conditions in the mine shafts stand as mute, unanswerable proof that the journey from and to the portal involves continuous physical and mental exertion as well as hazards to life and limb. And this compulsory travel occurs entirely on petitioners’ property and is at all times under their strict control and supervision.
*599Such travel, furthermore, is not primarily undertaken for the convenience of the miners and bears no relation whatever to their needs or to the distance between their homes and the mines.12 Rather the travel time is spent for the benefit of petitioners and their iron ore mining operations. The extraction of ore from these mines by its very nature necessitates dangerous travel in petitioners’ underground shafts in order to reach the working faces, where production actually occurs. Such hazardous travel is thus essential to petitioners’ production. It matters not that such travel is, in a strict sense, a nonproductive benefit. Nothing in the statute or in reason demands that every moment of an employee’s time devoted to the service of his employer shall be directly productive. Section 3 (j) of the Act expressly provides that it is sufficient if an employee is engaged in a process or occupation necessary to production. Hence employees engaged in such necessary but not directly productive activities as watching and guarding a building,13 waiting for work,14 and standing by on call15 have been held to be engaged in work necessary to production and entitled to the benefits of the Act. Iron ore miners traveling underground are no less engaged in a “process or occupation” necessary to actual production. They do more than “stand and wait,” Missouri, K. & T. Ry. Co. v. United States, 231 U. S. 112, 119. Cf. Bountiful Brick Co. v. Giles, 276 U. S. 154, 158. Theirs is a fossorial activity bearing all the indicia of hard labor.
*600The conclusion that underground travel in iron ore mines is work has also been reached by the Administrator of the Wage and Hour Division. On March 17, 1941, he approved an informal report of hia representative based upon an investigation of the “hours worked” in underground metal mines in the United States. The report concluded, in part, that “The workday in underground metal mining starts when the miner reports for duty as required at or near the collar [portal] of the mine and ends when he reaches the collar at the end of the shift.” See also Sunshine Mining Co. v. Carver, 41 F. Supp. 60. In addition, statutes of several important metal mining states provide that the eight-hour per day limitation upon work includes travel underground.16
Petitioners, however, rely mainly upon the alleged “immemorial custom and agreements arrived at by the practice of collective bargaining” which are said to establish “the 'face to face’ method as the standard and measure *601for computing working time in the iron ore industry.” They further claim that since the Eair Labor Standards Act contains no specific provision regarding underground travel in mines, Congress must be presumed to have intended to perpetuate existing customs or to leave the matter to be worked out through the process of collective bargaining.
The short answer is that the District Court was unable to find from the evidence that any such “immemorial” custom or collective bargaining agreements existed. That court, in making its findings, properly directed its attention solely to the evidence concerning petitioners’ iron ore mines and disregarded the customs and contracts in the coal mining industry. There was ample evidence that prior to the crucial date of the enactment of the statute, the provisions in petitioners’ contracts with their employees relating to a forty hour workweek “at the usual working place” bore no relation to the amount of time actually worked or the compensation received. Instead, working time and payment appear to have been related to the amount of iron ore mined each day. Hence such contract provisions defining the workweek are of little if any value in determining the workweek and compensation under a statute which requires that they be directly related to the actual work performed.
Likewise there was substantial, if not conclusive, evidence that prior to 1938 petitioners recognized no independent labor unions and engaged in no bona fide collective bargaining with an eye toward reaching agreements on the workweek. Contracts with company-dominated unions and discriminatory actions toward the independent unions are poor substitutes for “contracts fairly arrived at through the process of collective bargaining.” The wage payments and work on a tonnage basis, as well as the contract provisions as to the workweek, were all dictated by petitioners. The futile efforts by the miners *602to secure at least partial compensation for their travel time and their dissatisfaction with existing arrangements, moreover, negative the conclusion that there was any real custom as to the workweek and compensation therefor. A valid custom cannot be based on so turbulent and discordant a history; it requires something more than unilateral and arbitrary imposition of working conditions.17 We thus cannot say that the District Court’s findings as to custom and contract are so clearly erroneous as to compel us to disregard them.
But in any event it is immaterial that there may have been a prior custom or contract not to consider certain work within the compass of the workweek or not to compensate employees for certain portions of their work. The Fair Labor Standards Act was not designed to codify or perpetuate those customs and contracts which allow an employer to claim all of an employee’s time while compensating him for only a part of it. Congress intended, instead, to achieve a uniform national policy of guaranteeing compensation for all work or employment engaged in by employees covered by the Act.18 Any custom or contract falling short of that basic policy, like an agreement to pay less than the minimum wage requirements, cannot be utilized to deprive employees of their statutory *603rights. Cf. Overnight Motor Co. v. Missel, 316 U. S. 572; Holden v. Hardy, 169 U. S. 366. See also Louisville & Nashville R. Co. v. Mottley, 219 U. S. 467; J. I. Case Co. v. Labor Board, 321 U. S. 332; Order of Railroad Telegraphers v. Railway Express Agency, 321 U. S. 342.
This does not foreclose, of course, reasonable provisions of contract or custom governing the computation of work hours where precisely accurate computation is difficult or impossible. Nor are we concerned here with the effect that custom and contract may have in borderline cases where the other facts give rise to serious doubts as to whether certain activity or non-activity constitutes work or employment. It is sufficient in this case that the facts relating to underground travel in iron ore mines leave no uncertainty as to its character as work. The Act thus requires that appropriate compensation be paid for such work. Any other conclusion would deprive the iron ore miners of the just remuneration guaranteed them by the Act for contributing their time, liberty and strength primarily for the benefit of others.
The judgment of the court below is accordingly
Affirmed.
These actions were instituted under the Federal Declaratory Judgments Act, 48 Stat. 955, § 274D, 28 U. S. C. § 400. They were consolidated for trial purposes and the District Court entered a single judgment.
The “working face” is the place in the mine where the miners actually drill and load ore. The “face to face” basis of compensation, advocated by petitioners, includes only the time spent at the working face. The “portal to portal” basis, proposed by respondents, includes time spent in traveling between the portal or entrance to the mine and the working face and back again, as well as the time spent at the working face.
Since May 5, 1941, petitioners have paid their miners for travel. time pursuant to contract in compliance with the opinion of the Administrator of the Wage and Hour Division that underground travel in iron ore mines is work within the meaning of the Act.
No review has been sought of the exclusion from the workweek of the activities at the surface. We therefore do not discuss that issue in this case. Alexander v. Cosden Pipe Line Co., 290 U. S. 484, 487, and cases cited.
The Tennessee Coal, Iron & Railroad Company has eight mines; Sloss-Sheffield Steel & Iron Company, two mines; and Republic Steel Corporation, two mines.
As the District Court pointed out, the conditions set forth by the record are not intended to be used to censure petitioners’ manner of maintenance of their mines, “for these conditions may well be normal conditions in iron ore mines and practically inevitable.” Moreover, the record indicates that the Spaulding mine of the Republic Company has been operated only intermittently and experimentally during the last 20 years and many of the conditions in the other mines are not present. The ore is close to the surface and miners can walk all the way to the working faces.
One of the Tennessee Company’s superintendents stated that “Whenever a man comes to the mine late, dragging along and encourages others to be late, he is setting a bad example. I want this understood thoroughly—men must be on time; we don’t care whether they work here or not, but if they want to work here they will have to be on time or else they will be disciplined, even to discharge.”
The use of the bath house, or change house, is optional. Some miners change their clothes at home and make no use of the bath houses furnished by petitioners.
An ore skip is an ordinary four-wbeeled ore box car made of steel. It is normally used for transporting ore and its floor is often covered with muck from such haulings. When men are riding in the car it is known as a “man skip trip.” It is used for such purposes in the mines of the Tennessee Company and the Republic Company.
A regular man trip is a specially constructed series of ears. Each car is about eight feet long and resembles a stairway. Five men sit on either side of the car facing outwards, back to back with five men on the other side. The man trip used in the Sloss Company mines consists of six such cars.
Webster’s New International Dictionary (2d ed., unabridged) defines work as follows: “1. To exert oneself physically or mentally for a purpose, esp., in common speech, to exert oneself thus in doing something undertaken chiefly for gain, for improvement in one’s material, intellectual, or physical condition, or under compulsion of any kind, as distinguished from something undertaken primarily for pleasure, sport, or immediate gratification, or as merely incidental to other activities (as a disagreeable walk involved in going to see a friend, or the packing of a trunk for a pleasure trip) . . .” The word “employ” is defined as follows: “2. To make use of the services of; to give employment to; to entrust with some duty or behest.”
Cf. Dollar v. Caddo River Dumber Co., 43 F. Supp. 822; Sirmon v. Cron & Gracey Drilling Corp., 44 F. Supp. 29; Bulot v. Freeport Sulphur Co., 45 F. Supp. 380; Walling v. Peavy-Wilson Dumber Co., 49 F. Supp. 846.
Walton v. Southern Package Corp., 320 U. S. 540; Kirschbaum Co. v. Walling, 316 U. S. 517.
Fleming v. North Georgia Mfg. Co., 33 F. Supp. 1005; Travis v. Ray, 41 F. Supp. 6.
Walling v. Allied Messenger Service, 47 F. Supp. 773.
Arizona and Utah statutes specifically include all the travel time within the eight-hour limitation. Ariz. Code Ann. (1939), vol. 4, § 56-115; Utah Code Ann. (1943), § 49-3-2. The Supreme Court of Montana has construed Mont. Const., art. 18, § 4, and Mont. Rev. Code (1935), § 3071, which provide for eight hours of work per day in underground mines, to include all travel time, Butte Miners’ Union No. 1 v. Anaconda Copper Mining Co., 112 Mont. 418, 118 P. 2d 148. Nevada Comp. Laws (1929), § 10237, provides that the limitation shall apply to travel one way. But Wyoming Rev. Stat. (1931), § 63-107, specifically excludes underground travel from the limitation; a like result has been reached by interpretation of California Stats. 1909, ch. 181, p. 279, in Matter of Application of Martin, 157 Cal. 59, 106 P. 238. Alabama and Tennessee fix no limitation on hours, while maximum hour statutes of other metal mining states are inconclusive insofar as the inclusion of travel time is concerned. See also § 5 (2) of the English Metalliferous Mines Regulation Act (1872), 35 & 36 Vict., c. 77, which provides that “The period of each employment shall be deemed to begin at the time of leaving the surface, and to end at the time of returning to the surface.”
Blackstone has said that one of the requisites of a valid custom is that “it must have been peaceable, and acquiesced in; not subject to contention and dispute. For as customs owe their original to common consent, their being immemorially disputed, either at law or otherwise, is a proof that such consent was wanting.” 1 Commentaries 77. See also Pollock, First Book of Jurisprudence, 283 (6th ed.). <
Congress was not unaware of the effect that collective bargaining contracts might have on overtime pay. It expressly decided to give effect to two kinds of collective agreements, as specified in § 7 (b) (1) and (2) of the Act. Cf. § 8 (c). It thus did not intend that other collective agreements should relieve employers from paying for overtime in excess of an actual workweek of 40 hours, regardless of the provisions of such contracts.