No driver shall report for duty or remain on duty requiring the performance of safety-sensitive functions while having an alcohol concentration of 0.04 or greater. No employer having knowledge that a driver has an alcohol concentration of 0.04 or greater shall permit the driver to perform or continue to perform safety-sensitive functions. [66 FR 43103, Aug. 17, 2001, as amended at 77 FR 4483, Jan. 30, 2012]