The Fair Labor Standards Act is the federal law that requires employers to pay overtime to their employees. The Act applies to employers that have "annual gross volume of sales made or business done in excess of $500,000." The Act may also apply to individual employees if he or she is "engaged in commerce or the production of goods."
In Russell v. Continental Restaurant, Judge Williams dismissed a food-server's overtime claim because the restaurant she worked for (located in Montgomery County, Maryland) did not earn $500,000 in gross receipts. The Court also rules that the waitress was not engages in commerce even though she alleged served out-of-state customers.
Note, Maryland's overtime law does not apply to restaurants.