The U.S. labor shortage is so bad, employers have taken to stalking potential recruits in their favorite watering holes.

Evidence of how tight the labor market has become for employers seems to be everywhere. For example, seasonal holiday workers can expect their average hourly wage to jump 32 percent over last year, from $11.70 to $15.40, according to a survey of 1,000 retail, restaurant, and hospitality industry employers by Snag, an on-demand job scheduling service.

In tech, employers are even...