As coronavirus lockdowns begin to ease, the biggest fear among white-collar workers in the U.S. about returning to the office is their coworkers’ behavior, according to a new survey shared exclusively with Fortune.

Controlling employees’ behavior—including when they’re not in the office at all—is a thorny challenge. Workers may also be concerned about one another’s willingness to keep physical distance in the office, or to stay home if they feel sick.

“If your colleague is behaving in way that’s silly, they’re going to underground parties at night, that’s scary,” says Jamie Hodari, CEO of Industrious, an office space operator, which conducted the survey in partnership with the polling and data company Elucd.

Approximately 37% of office-going adults said that, when thinking about returning to the office, they are most concerned that “others in my office will behave in a way that puts me in danger.” By contrast, just 19% of respondents cited lax measures by their employer as their biggest concern about returning. Eleven percent were most worried about productivity under new health restrictions, and 8% were most concerned about the safety of their commute.

But a little more than a fourth of survey respondents (26%)—the second-largest group of respondents—said they had no concerns at all about returning to the office.

The results cast new light on the discourse around returning to the workplace during the coronavirus pandemic. Much of that has understandably focused on elements that employers and building operators can control, such as enhanced cleaning protocols, building ventilation, and redesigning offices to keep distance between workers.

“Some of this depends on density,” says Hodari, “But a lot of it depends on the way people behave and comply with protocols or not.”

Despite that anxiety, the survey found most workers are amenable to getting back to the office. Sixty percent of respondents said they were likely or very likely to return to the office when they had the option to do so.

The survey did find deviations between office workers in different circumstances. Above all, those who commute using public transit are substantially more hesitant to return to work than those who do not. Only 34% of public transit commuters said they were “very likely” to return to work when offices reopen, compared with 48% of non-transit commuters.

Office workers with kids at home were slightly more likely to want to get back to the office than those without kids: 48% of parents said they were “very likely” to return when offices reopened, compared with 45% of those without kids.

Hodari says the results highlight the diverse situations faced by workers as well as the need for flexibility from employers. “I really hope that most American businesses approach this as a question of employee choice,” he says. “There are going to be employees who live two blocks from the office and have no concerns, and there will be employees who can barely get their work done if you force them to come into the office, because they’re going to be riddled with anxiety and fear.”

The survey is the inaugural edition of a new data-gathering project called Workstat. The collaboration between Industrious and Elucd will conduct weekly surveys with an evolving set of questions about workers’ attitudes toward their workplace.

The current survey covers responses from 745 U.S. adults who worked in offices prior to the coronavirus crisis, weighted by demographic factors including age and race.