This job is non-union as he is a safety coordinator, but is registered with a union as an operator.
He was contracted through the company he works for, for the position and the job is from June to October 15th, then the scope of work is complete.
It appears that either route, going after the company, the guards, as well as just leaving it alone, has made clean to him that he will never have a job opportunity with these companies again.
The law protects your husband's reputation against defamation so, if someone defames him, he can sue the person for money to compensate him for damage to his reputation.
If your husband can prove that someone libeled him (that is written defamation) and that person does not have a good defence, then a court will presume that your husband suffered damages and award him money to compensate for his damaged reputation.
The law treats slander differently than libel: with slander (verbal defamation), your husband has to prove he suffered damages, in the form of financial loss, to get compensation. It can be very difficult to prove this sort of financial loss. That's why most slander cases never go to court.
But in the following four examples, a slander lawsuit may succeed without your husband proving financial loss. Even though there's no permanent record of the slander, the law will presume damages, as if there were libel, if someone: