No employer may knowingly allow, require, permit, or authorize a driver to operate a CMV in the United States in any of the following circumstances:
(a) During any period in which the driver does not have a current CLP or CDL or does not have a CLP or CDL with the proper class or endorsements. An employer may not use a driver to operate a CMV who violates any restriction on the driver's CLP or CDL.
(b) During any period in which the driver has a CLP or CDL disqualified by a State, has lost the right to operate a CMV in a State, or has been disqualified from operating a CMV.
(c) During any period in which the driver has more than one CLP or CDL.
(d) During any period in which the driver, or the CMV he/she is driving, or the motor carrier operation, is subject to an out-of-service order.
(e) In violation of a Federal, State, or local law or regulation pertaining to railroad-highway grade crossings.