WASHINGTON (AP) — The Supreme Court on Thursday used the case of a Christian mail carrier who did not want to work Sundays to solidify protections for workers who ask for religious accommodations.

In a unanimous decision the justices made clear that workers who ask for accommodations, such as taking the Sabbath off, should have their requests honored unless employers show that doing so would result in “substantial increased costs” to the business.

The court made clear that businesses must cite more than minor costs — known as “de minimis” costs — to reject requests for religious accommodations at work. Unlike most cases before the court, both sides in the case had agreed that businesses needed to show more.

At issue was a mail carrier in rural Pennsylvania, Gerald Groff, who was told that as part of his job, he would need to start delivering Amazon packages on Sundays. Groff declined, saying his Sundays are for church and family.

US Postal Service officials initially tried to get substitutes for Groff’s shifts, but they could not always accommodate him. When Groff did not show, that meant more work for others. Ultimately, Groff quit and then sued for religious discrimination.

The case is the latest religious confrontation that the high court has been asked to referee. In recent years, the court’s 6-3 conservative majority has been particularly sensitive to the concerns of religious plaintiffs. Last year, the court split along ideological lines in ruling for public high school football coach who wanted to pray on the field after games.

Other recent religious cases have drawn wide agreement among the justices, such as upholding a cross-shaped monument on public grounds and ruling that Boston violated the free speech rights of a conservative activist when it refused his request to fly a Christian flag on a City Hall flagpole.

A federal law, Title VII of the Civil Rights Act of 1964, requires employers to accommodate employees’ religious practices unless doing so would be an “undue hardship” for the business. But a 1977 Supreme Court case, Trans World Airlines v. Hardison, says in part that employers can deny religious accommodations to employees when they impose “more than a de minimis cost” on the business.

During arguments in Groff’s case in April the Biden administration’s top Supreme Court lawyer, Solicitor General Elizabeth Prelogar, representing the Postal Service, told the justices that the Hardison case as a whole actually requires an employer who wants to deny an accommodation to show more.

But Justice Samuel Alito wrote in the majority opinion that while some lower courts have understood Hardison the way the administration suggested, other courts incorrectly latched on to the “de minimis” language “as the governing standard.”

“In this case, both parties agree that the ‘de minimis’ test is not right, but they differ slightly in the alternative language they prefer. … We think it is enough to say that an employer must show that the burden of granting an accommodation would result in substantial increased costs in relation to the conduct of its particular business,” Alito wrote.

The administration has said that requests for religious accommodation come up most often when employees seek schedule changes such as having the Sabbath off or midday prayer breaks or exemptions from a company’s dress code or grooming policies. Other examples include employee wanting to display a religious symbol in the workplace.

The justices sent Groff’s case back to a lower court for another look in light of their decision.

For years, Groff was a fill-in mail carrier in Pennsylvania’s Amish Country who worked on days when other mail carriers were off. When an Amazon.com contract with the Postal Service required carriers to start delivering packages on Sundays, Groff balked.

To avoid the shifts, Groff initially transferred to a more rural post office not yet doing Sunday deliveries. Eventually, however, that post office was required to do them, too.

Whenever Groff was scheduled on a Sunday, a different carrier had to work or his spot went unfilled. Officials said Groff’s absences created a tense environment and contributed to morale problems. It also meant other carriers had to deliver more Sunday mail than they otherwise would.

Groff resigned in 2019 rather than wait to be fired. He sued the Postal Service for failing to accommodate his religious practice. Lower courts ruled against him.

Groff said in a statement after Thursday’s ruling that he was grateful the Supreme Court heard his case.

“I hope this decision allows others to be able to maintain their convictions without living in fear of losing their jobs because of what they believe,” he said.