This idea that the employer has the right to lord over the private lives of ordinary working people has got to go. Smoking weed in your off time isn't going to have an appreciable effect on your ability to operate heavy machinery.
If you have a good work record, and you show up on time ready and able to do the job, the employer should leave you alone.
If you have a good work record, and you show up on time ready and able to do the job, the employer should leave you alone.