The United States is a capitalistic society, currently structured in which non-union employees, or employees without a contract, are often considered to be employed "at will," or translated correctly, employed at the seemingly arbitrary will of their employer. That is to say, no matter how much a given employee appreciates their job and benefits, as well as their salary, and works hard, we find that in absence of an actual labor or contractual agreement that they are a party to, they can be terminated at any given moment for no reason, at all, by their employer and thereby become unemployed.
While there are indeed legislative laws which do provide employees with all sorts of rights, so that if an employee believes that they have been discriminated against or have been terminated illegally, which thus appears then to violate those rights, they do have some legal recourse. Additionally, there is the fact that those that are laid off or have been released from employment are often eligible for unemployment pay, which provides them with monetary benefits at a reduced portion of their salary amount for a finite period of time That said, though, the bottom line is that there are few people that ever welcome being let go, and many a person, when so losing their job, are not only stressed from such, but are soon put into a precarious financial situation.
The thing about financial responsibilities, is that those financial responsibilities and bills, are ever relentless, and therefore whenever an anticipated income stream is disrupted, the pressure to find a resolution to such is intensified. This is why, labor unions are so important to the working population, and obviously of immense importance to all those that labor within industries, in which they are seemingly easily replaceable. The fact that employees, have no security, and can be implicitly threatened with someone else to take their place or perhaps for some machine to perform their duties, or even with the closure of a given location, signifies that these employees are pretty much going to have to accept then whatever the labor conditions are for the job that they have.
This means that employers are in the catbird seat of determining the labor rate of their employees, the corresponding work conditions, and the labor hours and days to be worked by those employees. While any employee at any time, can state their case as to why they should make a higher wage, or request different hours, or desire more robust benefits; their voice, without a labor union backstopping them, is a lone voice, and often then, not only an ineffective voice, but could be a voice, that endangers their own employment.
The fact of the matter is, that millions of laboring Americans, don't have any logical reason to celebrate Labor Day, because they don't actually have any labor power, aren't going to have any labor power over their employer, ever, and are susceptible at any time of day, then, of being terminated from their employment, with possibly rather tragic consequences. Those that live in America deserve so much better, and in absence of a re-invigoration of actual labor unions, then the governance of this nation needs to be not only the employee of last resort for its people, but also see that all those that are employed are paid a living wage.