“The food-service sector is out of control,” said Eugene Lupario, chief executive of SVS Group, a staffing firm based in Oakland, Calif. “Employers are willing to pay almost anything they need to get workers.”

He said starting restaurant wages are nearing $20 an hour in the San Francisco area, from around $15 an hour before the pandemic. Some clients are willing to take workers who have already completed an eight-hour shift at another business, and pay them overtime wages to do so, Mr. Lupario said.