"Even where it's legal, Companies have the right to decide if they will tolerate usage in their employees."
Do they? Or rather should they.
Why is it that one's unalienable rights stop on the threshold of one's employer's parking lot?
Drug testing in the absence of proof of impairment is illegal under the 4th Amendment, or would be if corporations were not super-citizens.
Not sure how a maintenance worker, with a drug habit, can possibly afford a lawyer to take his case through the steps to a state SC appearance, especially since the charges were dismissed.
Although given the limited information in the article it was likely the state violated personnel policies in that the employee was not offered counseling/evaluation for a first offense.
Cases of this type usually hinge on the wording of the Employee Manual which often has an escalation of sanctions up to & including termination, jumping directly to termination without prior discipline problems often creates an actionable case, if you can afford effective legal representation which is beyond the reach of most citizens.