20 C.F.R. § 332.3
Subject to the provisions of § 332.2(b) , a day shall not be considered as a day of unemployment or as a day of sickness with respect to an employee if no remuneration is payable or accrues to him solely because of the application to him of a mileage or work restriction agreed upon in a written agreement between his employer and employees of his employer, or authorized pursuant to such written agreement. Provisions of agreements setting overtime or other premium rates of pay shall not be regarded as work restrictions. Mileage or work restrictions shall be considered as applicable to an employee with respect to any day on which he is out of service because of having reached or exceeded the maximum mileage, earnings, or hours of work prescribed in such an agreement, or authorized pursuant to such an agreement. Performance of other work by an employee while he is out of service because of having reached or exceeded the maximum mileage, earnings, or hours of work shall not serve to make the mileage or work restriction inapplicable to him.
20 C.F.R. §332.3