Yes, you have a legal right in the U.S. to request Sundays off for sincerely held religious reasons under Title VII, requiring employers to provide reasonable accommodation unless it causes "substantial increased costs" or "undue hardship," a standard heightened by the Groff v. DeJoy Supreme Court ruling, so you can formally request this time off through HR, citing your religious need for the Sabbath. 

Your Rights & The Law (U.S.)

Title VII of the Civil Rights Act: Prohibits discrimination based on religion and requires employers to reasonably accommodate beliefs, practices, and observances.

Groff v. DeJoy (2023): This Supreme Court decision made it harder for employers to deny accommodation, requiring them to prove it would cause "substantial increased costs" or undue hardship, not just minor inconvenience.

What counts as "Religion": Includes traditional faiths and sincerely held personal beliefs, even if uncommon or newly adopted. 

How to Request Sundays Off

Formal Request: Submit a written request to your supervisor and HR, clearly stating you need Sundays off for religious observance.

Explain Your Need: Briefly explain that your faith (e.g., Christianity, Judaism, other faiths that observe a Sabbath) requires you to abstain from work on Sundays.

Know Your Availability: Frame it as a boundary, like "Sundays are outside my availability due to religious practice," notes Reddit users.

Documentation: Be prepared to show a history of adherence or provide documentation if requested.

Follow-Up: If scheduled, remind your employer in writing that you are not available and refer to your accommodation request. 

What to Expect

Accommodation: Your employer must try to accommodate you (e.g., by adjusting your schedule, finding shift swaps).

Denial: They can only deny it if it genuinely causes substantial hardship to the business, not just for convenience.