Employees at Juul Labs Inc. were accustomed to puffing away on the sleek e-cigarettes that made the startup an overnight success. So their boss had to acknowledge some awkwardness on Tuesday when he delivered the message: No vaping in the office.

Juul’s chief told employees across the U.S. that, starting immediately, they could no longer use its products inside at work and that future vaping at San Francisco headquarters must happen outside under a tent to be erected specifically for the purpose.