Trans World Airlines, Inc. v. Hardison
Trans World Airlines, Inc. v. Hardison, 432 U.S. 63 (1977), is a landmark decision on religious liberty and employment law. In 1977, the US Supreme Court held that an employer may discharge an employee who observes a seventh-day sabbath, and that such employee is not entitled to equal employment opportunity protection under Title VII of the Civil Rights Act of 1964, which makes it an unlawful employment practice for an employer to discriminate against an employee on the basis of his religion. However, subsequent legal developments and cases have challenged this precedent's validity. Case History
Larry Hardison was an employee at Trans World Airline. Hardison was a member of the Worldwide Church of God and refused to work on Saturdays which was his sabbath. TWA transferred him from the night shift to the daytime on Saturdays. However, his seniority was affected by the shift change, and the union did not allow him to take Saturdays off. TWA declined a proposal for him to work a four-day week and ultimately discharged him for refusing to work on Saturdays. Supreme Court Decision 
The Supreme Court sided with Trans World Airlines, stating that the Equal Employment Opportunity Commission requires "reasonable" accommodations for religious exercise. Justice Thurgood Marshall, in a widely-cited dissent, wrote, "[O]ne of this Nation's pillars of strength, our hospitality to religious diversity, has been seriously eroded." Challenges to the legal precedent 

Various challenges to the TWA v. Hardison precedent have emerged over time. In 2020, the Supreme Court declined to review Patterson v. Walgreen, a case which might have led to a reconsideration of the TWA v. Hardison precedent. Justice Alito, joined by Justices Thomas and Gorsuch, wrote a statement calling for the Hardison precedent to be reconsidered in a future appropriate case:

Similarly, in 2021, the Supreme Court denied certiorari in Dalberiste v. GLE Associates and Small v. Memphis Light, Gas & Water, cases that potentially challenged the established precedent. Justices Gorsuch and Alito wrote a dissent to the denial of certiorari. On September 26, 2022, 15 members of the US Congress filed an amicus brief arguing that the standard in Hardison for "undue hardship" conflicted with the text and legislative purpose of Title VII. They urged the court to grant certiorari in Groff v. DeJoy and overturn the standing precedent. Groff v. DeJoy

The Supreme Court discussed the Groff v. DeJoy case in their conference on January 13, 2023, and granted certiorari. This case challenges the legal precedent from TWA. The precedential value of Hardison is now lessened by: GROFF v. DEJOY, POSTMASTER GENERAL per this controlling language located at Part II C final paragraph; of the Opinion of the Court. See also 
 Estate of Thornton v. Caldor, Inc., 1985
 Sunday closing law

References

United States labor case law
Trans World Airlines
United States Supreme Court cases
United States Supreme Court cases of the Burger Court
1977 in United States case law
United States civil rights case law