By Nicholas Bloom, Harvard Business Review

As U.S. states and the federal government start to roll back Covid-19 restrictions, and companies and workers start to firm up their office return plans, one point is becoming clear: The future of working from home (WFH) is hybrid. In research with my colleagues Jose Maria Barrero and Steven J. Davis, as well as discussions with hundreds of managers across different industries, I’m finding that about 70% of firms, from tiny companies to massive multinationals like Google, Citi, and HSBC, plan to move to some form of hybrid working.

But another question is controversial: How much choice should workers have in the matter?

On the one hand, many managers are passionate that their employees should determine their own schedule. We’ve been surveying more than 30,000 Americans monthly since May 2020 and our research data shows that post-pandemic, 32% of employees say they never want to return to working in the office. These are often employees with young kids, who live in the suburbs, for whom the commute is painful and home can be rather pleasant. At the other extreme, 21% tell us they never want to spend another day working from home. These are often young single employees or empty nesters in city center apartments.

Given such radically different views it seems natural to let them choose. One manager told me “I treat my team like adults. They get to decide when and where they work, as long as they get their jobs done.”

But others raise two concerns — concerns, which after talking to hundreds of organizations over the last year, have led me to change my advice from supporting to being against employees’ choosing their own WFH days.

One concern is managing a hybrid team, where some people are at home and others are at the office. I hear endless anxiety about this generating an office in-group and a home out-group. For example, employees at home can see glances or whispering in the office conference room but can’t tell exactly what is going on. Even when firms try to avoid this by requiring office employees to take video calls from their desks, home employees have told me that they can still feel excluded. They know after the meeting ends the folks in the office may chat in the corridor or go grab a coffee together.

The second concern is the risk to diversity. It turns out that who wants to work from home after the pandemic is not random. In our research we find, for example, that among college graduates with young children women want to work from home full-time almost 50% more than men.

This is worrying given the evidence that working from home while your colleagues are in the office can be highly damaging to your career. In a 2014 study I ran in China in a large multinational we randomized 250 volunteers into a group that worked remotely for four days a week and another group that remained in the office full time. We found that WFH employees had a 50% lower rate of promotion after 21 months compared to their office colleagues. This huge WFH promotion penalty chimes with comments I’ve heard over the years from managers. They often confided that home-based employees in their teams get passed over on promotions because they are out of touch with the office.

Adding this up you can see how allowing employees to choose their WFH schedules could contribute to a diversity crisis. Single young men could all choose to come into the office five days a week and rocket up the firm, while employees with young children, particularly women, who choose to WFH for several days each week are held back. This would be both a diversity loss and a legal time bomb for companies.

So I have changed my mind and started advising firms that managers should decide which days their team should WFH. For example, if the manager picks WFH on Wednesday and Friday, everyone would come in on the other days. The only exceptions should be new hires, who should come in for an extra office day each week for their first year in order to bond with other new recruits.

Of course, firms that want to efficiently use their office space will need to centrally manage which teams come in on which days. Otherwise, the building will be empty on Monday and Friday — when everyone wants to WFH — and overcrowded mid-week. To encourage coordination, companies should also make sure that teams that often work together have at least two days of overlap in the office.

The pandemic has started a revolution in how we work, and our research shows this can make firms more productive and employees happier. But like all revolutions this is difficult to navigate, and firms need leadership from the top to ensure their work force remains diverse and truly inclusive.