There are State labor laws as well as Federal labor laws, so what laws are applicable for the protection and benefit of workers, is dependent upon the actual State that you live in, though on a Federal basis, there are minimums in regards to pay rate and overtime rates that have been set by law, that must therefore be adhered to, such as the minimum wage per hour, though that has exceptions to it, as well as overtime, which also has exceptions to it. Over and above the pay rate structure, as well as rules in regards to overtime and hours worked per week, before overtime is applied, are the actual hours that a given worker is entitled to have on a weekly basis, in which, unless a worker is categorized as, for example, those with a H-2B visa, then such employees in absence of a written contract that stipulates a minimum amount of hours due to them, or are hired as exempt employees at a certain pay rate per week, aren't guaranteed work hours by any sort of governmental fiat, but instead are under the aegis of the company policy of the company that they work for, so that those that are in low-wage jobs, work under conditions in which there typically is no formal commitment made by the employer for total hours to be worked, weekly.
That is to say, when one is employed at a fast food company, in which, there is no labor union, and pay has been set at a certain rate, the hours that one works in total, the hours that one works on a given day, and the scheduling of working hours, are all made essentially at the discretion of the company, itself, so that if one can barely survive, when they work forty hours a week, the fact, that this present job, will not guarantee a certain amount of hours, unless written into their policy, such as forty hours, means that in all likelihood, forty hours probably won't be worked in a week, and the shortfall may be substantially more than that. Adding further injury to the employment situation, while companies may well take into consideration, responsibilities one may have in regards to school, family life, such as children and their care, commute time, and various other factors, for the most part, as the employer, they will dictate to their employees, what hours that one is required to work, which may be provided to employees, two weeks in advance, or literally a day or two in advance, and it is therefore that employee's responsibility to work those hours, though, most companies allow its employees to trade shifts with other employees, even through the usage of apps to aid such, with managerial approval.
The fact that as an employee one does not have a set guarantee of at least minimum hours, though you might be promised a minimum, nor does one have a set working schedule that is consistent and under the employee's control or input, though some companies are much more consistent than others, makes it difficult to not only take care of one's personal life and other responsibilities, but also difficult to secure another job with another company, because one's availability to one company or another, will be impacted by one's lack of control over the scheduling of one's work hours.
All of these things come forth from the fact, that labor laws, as currently written, do not empower employees to receive a minimum amount of hours, or a consistent work schedule, which instead are left to the discretion of the employer. This effectively signifies that without the power and unity of labor unions, one person is not going to be able to effect change, because the employer will simply terminate that person, without consequences. While minimum wage laws have their place, there should also be a requirement from employers of a minimum amount of hourly work employees receive weekly, as well as consistency in the scheduling of work hours, that is agreed upon, by both parties. In order for these things to occur, labor unions are necessary, for in numbers there is strength, and according to bls.gov, there are 2.6 million workers with wages at or below the federal minimum wage, in which employees besides getting short shrift from the wages paid, aren't even guaranteed minimum hours of work, as well as their scheduling of their work hours, being controlled by their employer, so that, unless unionized, this won't change.