A Christian U.S. Postal Service worker who requested to not work on Sundays won a unanimous victory at the Supreme Court on Thursday in a decision that makes it easier for employees to seek religious accommodations. 

The decision clarifies a decades-old precedent that governed when the Civil Rights Act of 1964 requires businesses to accommodate their employees’ religious beliefs.

Conservative Justice Samuel Alito wrote that businesses must provide an accommodation unless it would impose “substantial increased costs.”

“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.

Gerald Groff, who said working on Sundays violates his religious beliefs to rest during the Sabbath, sued the U.S. Postal Service after being disciplined for missing scheduled Sunday shifts to deliver Amazon packages. 

The Postal Service originally did not require Groff to work on Sundays until it contracted with Amazon to deliver packages on that day of the week. 

The postmaster accommodated Groff for some time by either skipping him in the Sunday rotation or automatically scheduling an extra person. The agency later ended the accommodation and instead asked for volunteers in Groff’s place. When no one volunteered, Groff received repeated discipline for more than 24 absences over two years.

Groff was expected to soon be fired, so he instead resigned and sued the agency.

The court’s decision effectively revives his attempt, but the justices sent his case back to a lower court for additional consideration based on the clarified standard.

“I am grateful to have had my case heard by the U.S. Supreme Court and that they have decided to uphold religious liberty,” Groff said in a statement. “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.”

Under Title VII of the Civil Rights Act of 1964, businesses must reasonably accommodate an employee’s religious observance unless it would impose an “undue hardship on the conduct of the employer’s business.”

In 1977, the Supreme Court in Trans World Airlines Inc. v. Hardison defined “undue hardship” as “more than a de minimis burden,” the Latin term for minimal.

Both Groff and the Justice Department agreed the standard shouldn’t be taken literally. But they sparred before the justices on the new verbiage the court should replace it with and whether Hardison should be outright overturned.

After turning away multiple requests to revisit the decades-old standard in the past, the court has now heightened the test — but did not overturn the Hardison decision — adding to a string of decisions that have expanded religious rights under the First Amendment and other laws.

Groff wanted the 1977 decision overturned and replaced with a “significant difficulty or expense” standard. Various religious groups, 10 Republican members of Congress and 22 Republican state attorneys general backed Groff’s appeal before the high court.

The Justice Department urged the court to instead update and reinforce Hardison, warning that explicitly disavowing it would disrupt decades of case law that has relied upon it. The American Postal Workers Union, 11 Democratic state attorneys general and various atheist groups supported the Justice Department.

The sides also sparred over whether businesses can cite burdens on other employees when rejecting an accommodation request. The lower court had ruled that exempting Groff from working on Sundays would have imposed burdens on his coworkers by disrupting the workflow and diminishing employee morale.

The high court ruled that impacts on coworkers are relevant only to the extent those impacts go on to affect the conduct of the business.