Union is a fact everywhere. It is more aggressive where a grievance redressal mechanism is absent. Therefore, it becomes a priority of every HR/ Personnel manager to address the grievance of the employees failing which they will go for a collectively resulting in forming a trade union. Each individual employee should be given an opportunity to open up about his grievance and you should find a solution for it. Otherwise, what happens is that each one will start discussing the issues in a common forum and will find that only when they demand collectively their grievances would get redressed. The legal form of it is called trade union. It is a fact and some employers will put the entire blame on the Personnel/ HR manager and even the HR person would have to leave the organisation. This can be avoided if the employer is sympathetic towards the employees. The HR person can escalate or report the issues and the employer can step in and solve the issues. If not done, HR will become helpless.
Please find that you have a system of addressing the individual grievances and if not, please start it. Give a message that their grievances will be taken up in priority,