Many companies regularly look up job applicants online as part of the hiring process. A new study suggests they may also use what they find to discriminate.

The study, a Carnegie Mellon University experiment involving dummy résumés and social-media profiles, found that between 10% and a third of U.S. firms searched social networks for job applicants' information early in the hiring process. In those cases, candidates whose public Facebook profiles indicated they were Muslim were less likely to be called for interviews than...