We have had an incident where union workers in a trade were supposedly advised by their union hall to not converse with the only non-union guy from that is from their trade on the same shift. Our HR policy is that systematic exclusion is a form of bullying and so some action must be taken. I've talked to my boss and we are switching the excluded guy to a shift with others from the same contractor but are not taking action against the excluders because in the end it is a he said/she said situation. We have reached a resolution in this situation but I'm wondering how to avoid it in the future.
We had a situation where people are being needlessly cruel to someone for being a non-member of their group. In this circumstance we did not have enough evidence to take action against his antagonists. In your opinion how can I prevent situations of this nature from recurring in the future?
Was it an error mixing union and non-union workers to begin with? When in a mixed union/non-union shop what are some strategies to prevent friction between the groups?