Federal law (the Jury Systems Improvement Act, 28 U.S.C. § 1875) makes it illegal for an employer to fire, threaten, or penalize an employee for serving on a federal jury. It does not require the employer to pay for that time. State law governs state jury service and any pay rules.
Jury duty rules in the U.S.
What to do if you're summoned
Tell your employer as soon as you get a jury summons and keep a copy. Your job is protected in every state, so you cannot be fired or disciplined for serving. Courts pay a small daily juror fee plus mileage, separate from any wages. If your employer retaliates, you can usually file a complaint with the court that summoned you or your state labor office. This is general information, not legal advice.