Well first, many probably aren't using them right and are exposing themselves to lawsuits. Second, no law prevents an employer from paying any employee a salary, what the law prohibits is paying a non-exempt employee a salary without paying overtime for hours worked in excess of 40 per week. So, if the employee does not go over 40 hours, paying them a flat salary does not violate any law.
But aside from these considerations, chefs and sous chefs who have attained a four-year specialized academic degree in a culinary arts program, generally meet the duties requirements for the "learned professional" exemption from overtime. The DOL clarifies that the learned professional exemption is not available to cooks who perform predominantly routine mental, manual, mechanical or physical work” (29 C.F.R. §541.301(e)(6)) But this exemption is often used as the basis for salary exemption for chefs in "fine dining."
Certain other chefs also spend most of their time coordinating the work of the cooks and directing the preparation of meals, which qualifies them for the managerial exemption as discussed above.
So, there are certainly ways for chefs and sous chefs to be salary exempt. There are also certainly many who are classified as salaried exempt
but not properly. I think this would explain how restaurants around the country using salaried chefs and sous chefs.
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