DOT Rule 49 CFR Part 40 Section 40.191 defines specific employee behaviors—such as failing to appear, leaving the site, or tampering with a specimen—that constitute a refusal to take a drug test. This regulation mandates that a refusal is treated as a positive result, requiring immediate removal from safety-sensitive duties. For more details, visit U.S. Department of Transportation . DOT Rule 49 CFR Part 40 Section 40.191