We are asked this question a lot. The answer is 100% up to the employer and should be described in the employer’s written substance abuse policy.
For regulated employees (such as truck drivers with CDLs), the DOT regulations do not address hiring, termination, or other employment actions. These decisions are solely the employer’s, which may be based on company policy and/or any collective bargaining agreements.
If you need to know, ask the employer. Some will terminate or refuse to hire. Some might offer a second chance.