Companies are trying to arrange the safe return of workers to big-city offices, but one factor remains beyond their control: the mass-transit commute.

Many workers say they are reluctant to ride subways, trains and buses into city centers, particularly when they could be in close quarters with unmasked or unvaccinated people. Several executives say their employees are citing Covid-19 fears related to their commutes as a key reason they want to continue working from home.