[Volundr]

Assuming you are in the US, they can't require any notice. In most other countries to the best of my knowledge, but your local laws may vary.

A company can certainly ask you to give more notice, but you are under no obligation to do so.

[tptacek]

You could in theory have an employment contract that requires notice. But it probably wouldn't have much force; such a contract would establish that failing to give notice would be a breach of contract, and you could theoretically be on the hook for making your employer whole for the "harm" you caused, but unless you were given some significant consideration for your side of the contract --- a signing bonus or something, maybe? --- the harm your employer could demonstrate in court would be so minimal that the cost of enforcing the contract would far outweigh the return they'd get from enforcing it.†

In practice: a pretty rare situation, and not a meaningful deterrent to quitting at will.

I believe the cases where you're meaningfully prevented from quitting without giving notice, generally, are cases where you already know clearly that you can't, and why you can't, because you negotiated your contract and know what you'd be giving up to leave. There are key-person agreements that get signed in acquisitions that have that kind of effect.

Employees, though? Not so much. Employers in the US that purport to require notice from rank and file are pretty much generally full of shit.

(Not a lawyer, have just seen a lot of weird employment situations).

† Signing bonus claw-backs are also super common outside of "notice" situations, so it's not like that's an exotic case; if you have a signing or retention bonus, you probably already know you have a contract requiring you to return it if you leave within N months.