Federal civil rights law requires employers to accommodate their employees’ religious needs unless the request would impose “undue hardship on the conduct of the employer’s business.” Congress didn’t bother to define “undue hardship,” so 46 years ago the Supreme Court came up with a definition of its own.

An accommodation requiring an employer “to bear more than a de minimis cost” — meaning a small or trifling cost — need not be granted, the court said in Trans World Airlines v. Hardison. In that case, an airline maintenance worker claimed a legal right to avoid Saturday shifts so he could observe the tenets of the Worldwide Church of God, which he had recently joined. Ruling for the airline, the court noted that if one worker got Saturdays off for religion reasons, the burden would fall on other workers who might have nonreligious reasons for wanting to have the weekend off.

“We will not readily construe the statute to require an employer to discriminate against some employees in order to enable others to observe their Sabbath,” the court said.

Treating religion as nothing particularly special, the decision reflected the spirit of the times but was deeply unpopular in religious circles. There have been many attempts over many years to persuade Congress to amend the law, Title VII of the Civil Rights Act of 1964, to shift the balance explicitly in favor of religiously observant employees. Between 1994 and 2019, more than a dozen such bills were introduced. None emerged from Congress.

And so now, a very different court from the one that ruled 46 years ago is about to do the work itself.

That isn’t an idle prediction but rather the surely foreordained outcome of the new case the justices recently added to their calendar for decision during the current term. The appeal was brought by a conservative Christian litigating group, First Liberty Institute, on behalf of a former postal worker, Gerald Groff, described as a Christian who regards Sunday as a day for “worship and rest.”

Mr. Groff claimed a legal right to avoid the Sunday shifts required during peak season at the post office where he worked. Facing discipline for failing to show up for his assigned shifts, he quit and filed a lawsuit. The lower courts ruled against him, with the Philadelphia-based U.S. Court of Appeals for the Third Circuit expressing no doubt that the disruption and loss of morale Mr. Groff’s absences caused in the small rural post office where he worked exceeded the de minimis threshold that the Supreme Court’s 1977 precedent requires an employer to demonstrate.