Some people have contracts. Union workers do but a lot of that is blue collar work. Assembly lines, plumbers, electricians etc. white collar work is mostly “at will” which means workers don’t need a reason and either do companies for leaving. Also means you don’t need notice like two weeks. In reality it doesn’t work that way. Most people give two or more weeks notice and companies mostly tell people they are being laid off ahead of time. Some are generous with severance pay. But really companies can do whatever they want. Change pay, responsibilities, benefits etc without notice