Most states, and I suspect all, forbid employers from punishing employees for appearing in court pursuant to subpoenas.
Quote Quoting California Labor Code, Sec. 230(b)
(b) An employer shall not discharge or in any manner discriminate or retaliate against an employee, including, but not limited to, an employee who is a victim of a crime, for taking time off to appear in court to comply with a subpoena or other court order as a witness in any judicial proceeding.