Wear Your Mask. Please. No, Not on Your Chin.

KEY WEST, Fla. — Rachel Kobylas longs for the days when her job as a code enforcement officer in the laid-back Florida town of Key West meant that she drove around making sure people turned off noisy power tools after 7 p.m.

She went after overgrown grass, unpermitted construction and boats illegally parked on the street. That all changed this summer, when her main challenge became convincing the tourists, bartenders, T-shirt shop sales clerks and fishermen who flock along Key West’s sweltering streets in shorts and flip-flops that they should also be wearing a mask.

And not just on their chin.

“There have been some really negative interactions,” said Ms. Kobylas, 35, describing the “series of expletives” she routinely confronts, particularly on social media, when she tries to enforce the city’s mask ordinance. “We do our best to be firm but fair and respectful.”

Key West, a city of about 25,000 on the southernmost edge of the continental United States, managed to hold off the coronavirus for several months after the county put checkpoints on the only road into town, keeping visitors out.