Severance is never a requirement of any employer unless you have a signed employment agreement stating otherwise, or, it is a written policy of the company.
Lack of Voluntary Consent: Under California law, a severance agreement can be considered valid and enforceable only if the parties entered into it voluntarily. If your consent was obtained through coercion, duress, or fraud, the agreement will be deemed invalid.
Neither the California Labor Code nor the federal Fair Labor Standards Act require employers to offer severance agreements to departing employees. Instead, severance agreements are provided by employers to accomplish a specific goal.
Employers are not legally required to offer severance during layoffs, but many choose to do so to maintain goodwill and ease the transition for their former employees. If you are offered a severance agreement, remember that you don't have to sign it right away.
It makes no difference how long you've been with a company so yes, it's legal to lay off any and everyone without severance. The exceptions: a union agreement requiring severance, a personal contract calling for a severance. This is usually only for executives and ``key'' people.
Severance packages are typically offered to executives and employees who are laid off due to downsizing or restructuring. They are not usually offered to people who resign or who are fired for poor performance or other causes.