The Supreme Court on Thursday ruled in favor of an ex-postal worker who challenged the U.S. Postal Service for refusing to back his religious accommodation not to work on the Sabbath.

The unanimous ruling clarified a half-century precedent, explaining that when an employer denies an employee a religious accommodation, the employer must show a substantial cost for the adjustment.

Under the prior precedent dating to 1977, lower courts sided with employers so long as they showed even a de minimis, or trivial, cost to accommodating an employee’s request.

“We hold that showing ‘more than a de minimis cost,’ as that phrase is used in common parlance, does not suffice,” wrote Justice Samuel A. Alito Jr. for the court.

The case before the court involved Gerald Groff, a former mail carrier in Pennsylvania’s Amish Country who was pressured to work Sundays after the Postal Service took a delivery contract with Amazon. Mr. Groff asked not to be scheduled on those days for religious reasons, but the post office said it couldn’t always find substitutes.

Mr. Groff was punished for missing work and eventually left the job and sued.

Lower courts said the Postal Service was protected under a 1977 ruling in Trans World Airlines v. Hardison, which held that employers can deny religious requests when a business experiences an “undue hardship” from accommodating the employee.

The 3rd U.S. Circuit Court of Appeals said employees at the small location where Mr. Groff worked would have to bear too much burden to accommodate him.

The high court’s ruling Thursday reverses the 3rd Circuit’s decision and further explains its precedent in Trans World Airlines v. Hardison, giving employers a tougher standard to meet when denying employees’ religious requests.

• Stephen Dinan can be reached at sdinan@washingtontimes.com.

• Alex Swoyer can be reached at aswoyer@washingtontimes.com.