519.21.1. No operator, shipper, consignee or other person shall request, require or allow a driver to drive(1) if the driver’s driving ability is impaired to the point where it is unsafe for the driver to drive ;
(2) if driving jeopardizes or is likely to jeopardize the safety or health of the public, the driver or the employees of the operator ;
(3) if the driver is the subject of an out-of-service declaration under section 519.12 ; or
(4) other than in accordance with the provisions of sections 519.9 and 519.10.
A government regulation determines the circumstances under which subparagraphs 1 to 4 of the first paragraph apply