49 C.F.R. § 219.619
Positive alcohol and drug test results and refusals; procedures
Section 219.104 contains the procedures for administrative handling by the railroad or contractor in the event a body fluid specimen provided under this subpart is reported as a verified positive by the Medical Review Officer, a breath alcohol specimen is reported at 0.04 or greater by the Breath Alcohol Technician, or a refusal to test has occurred. The responsive action required in § 219.104 is not stayed pending the result of the testing of a split body fluid specimen or a challenge to any part of the testing process or procedure.