WASHINGTON—The Supreme Court on Monday buttressed religious expression at the workplace, ruling for a Muslim job applicant Abercrombie & Fitch Co. rejected because she wore a head scarf.

The 8-1 decision underscored employers’ obligation to accommodate, within reason, the religious practices of workers and applicants unless they impose an “undue hardship” on the business. It is the latest in a line of Supreme Court cases that have elevated religious rights over secular interests, whether exercised by powerful corporations,...