Warren Bischoff, who leads a group of financial advisers in the Washington, D.C., area, has taken on a new role since returning to the office a few months ago. He’s the dress-code police.

In a single week, he had to tell one employee that white tennis sneakers are a no-no, another that bluejeans aren’t appropriate, and a third that T-shirts will never fly. In a recent edge-case ruling, he decided that “dress sneakers”—brown shoes with a white sole—might be OK, but only on Fridays.

“They have a foot in both camps,” he says. “They’re very tricky.”