I am currently under re-investigation for my public trust. I have been a contractor for 5 years. I met with the investigator and she wanted to reach out to my last employer and supervisor again. They had nothing to do with clearances or the government. Anyway this was obviously done the first time around before I was hired. I kept in touch with my old supervisor and because he has another job now he was unable to meet with her when she wanted. And my old place of employment wasn’t exactly full of friendly staff. If she couldn’t meet with my previous supervisor and shows up to unfavorable staff at my last job will that likely affect me? Like I said I’m already employed and have been for 5 years.
If they can’t get in touch with those folks they’ll try to find someone else. They will also (depending on the requirements of the investigation type or “tier”) go to HR and want to look at your employment records for any indication of disciplinary action. But this would not be the first time that something like this has happened. I for one do not think it will be a problem.
It doesn’t matter if your last employer was government related or not. If they fall within the coverage period then they will be contacted. During your initial interview you are asked if you had any personality conflicts at any of your employments. That question is there for a reason. Name drop if you seriously had problems with someone who would talk negatively about you. I have interviewed coworkers who weren’t necessarily fond of their coworker and it never ended badly. The people were honest and the questions are very direct and straight forward. They’re asked about moral character integrity etc. they’re not asked if they liked you or didn’t like you. I wouldn’t worry too much about it.