I've had non-union shops change passwords, install jumpers, and change parameters on jobs they've lost. I have yet to experience this when taking over a union job. I can only assume what I have found is sabotage, there is the outside change it was due to gross incompetence. In only one particular case I know it was sabotage, but the culprit is no longer in business.
I work for a top tier union company, we loose jobs and pick up jobs, and sabotage is not worth it. Our reputation is far more important than a job here and there.
While it's easy to trash talk the morals of non-union workers, sometimes it's more ignorance than it is sabotage. We took on a power station where the elevators were previously looked after by anyone on site that could keep it running. Found a gate switch jumped out only because an electrician could troubleshoot well enough to find out where the power stopped... Changed a set of ECI contacts and everything was good again. He wasn't trying to kill anyone (although, he came closer than he realized) but he just didn't know enough to even step foot in the machine room.
