In the US you have no such guarantee, it's completely at the pleasure of your employer.

I could walk into work this morning, get laid off, and escorted out of the building without notice. That's it, done, no more salary. To make it even worse, you also lose the subsidized health insurance. My employer pays about 60% of the cost for my family, so my monthly premiums would jump from $800 to nearly $2000 a month at the same time my income drops to near zero.

Sure there's unemployment payments, but they're usually only a fraction of your previous salary, and are often capped to a maximum by your individual state.

Welcome to capitalism ;)