The Federal Motor Carrier Safety Regulations address use of alcohol by any commercial driver (>10,000lbs MGVWR) in CFR 392.5:

No driver shall—

Use alcohol, as defined in CFR 382.107 of this subchapter, or be under the influence of alcohol, within 4 hours before going on duty or operating, or having physical control of, a commercial motor vehicle; or use alcohol, be under the influence of alcohol, or have any measured alcohol concentration or detected presence of alcohol, while on duty, or operating, or in physical control of a commercial motor vehicle.

There are additional provisions to this regulation, please read CFR 392.5 in its entirety.

Any driver who is found to be in violation of these regulations shall be placed out-of-service immediately for a period of 24 hours.

Additional FMCSR Regulations apply to drivers who are operating a CMV with a CDL and can be found in and CFR 382 such as random, post accident and reasonable suspicion testing. CFR 383.51 addresses disqualification of a CDL for alcohol violations in a CMV and a NON-CMV.

The bottom line is that a driver of a commercial motor vehicle jeopardizes his/her license and job anytime they drive any type of motor vehicle under the influence of Alcohol.