Legal Question in Employment Law in California

It's very tacky, but not illegal. You must receive your final pay within the statutory period, however. Otherwise, waiting time penalties can be assessed.

They can use any means that conveys the message to you. They owe your last check within one day of firing. In general, unless you are civil service, in a union or have a written employment contract, you are an 'at will' employee that can be disciplined or fired any time for any reason, other than illegal discrimination under the Civil Rights, or Whistle-blower, or similar statutes. Your goal should be to keep your employer happy with you.