Familiar dividing lines are taking shape in a new federal appeals court case from Missouri that confronts the scope of workplace protections for gay, lesbian and bisexual workers.

Major U.S. companies including Microsoft Corp., Airbnb Inc., eBay Inc., and Viacom Inc. are backing the worker, a health care specialist named Mark Horton who sued St. Louis-based Midwest Geriatric Management for allegedly pulling his job offer when they discovered he is gay.