Under California law, employer must provide to employee: Notice to Employee As To Change In Relationship, Final Paycheck, Notification of Coverage Options, Notice of COBRA Continuation Rights, COBRA Election Notice, HIPP Notice, and Notice of Retirement Benefits.
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.
You are not required to accept the deal the employer initially offers. As with other types of contracts, the help of experienced counsel can influence the terms of the agreement. No federal law requires an employer to offer severance packages to laid-off employees under all circumstances.