There is an implied 2 week notice that all workers have when changing jobs. In a market where the employee has the advantage, the employer will have to adapt or lose the employee. In a market where the employer has all the advantage, the employee will have to adapt as well. However, the ability of an employer to survive the loss of one employee is far greater than the loss of a job by any single employee in an at will contract. If you actually care more about people than money, the choice is simple.
seldom have I ever been given a two weeks notice, so seldom I can't ever remember one. I have seen where employers want a two weeks notice, even require it. My kid just got told to be back to work on Friday last week, he worked Friday, sat and Sunday night only to be told he wasn't needed on Monday morning at 8:00 am. Three of them were laid off with no notice.
all a union does is make a company to have a set of rules they must follow, not just a set of rules that an employee has to follow. And the truth is a company has a set of rules, which they can get rid of, change or add to at anytime before or after the fact.
I understand to someone running a company that may be a problem they don't want, but for an employee that is something that allows them to sleep at night knowing they have someone on their side.