When employees are upset, management becomes upset, which causes employees to become more upset, which causes management to become more upset.... Fortunately, there are ways to stop this freewheeling cycle.
Your first step was the correct one. When the employees appear to be angry and negative, it makes sense to meet with them and attempt to clear the air. However, since you feel like you are still in the fog when it comes to understanding the negativity, a related step is to meet with the employees whom you consider to be the opinion leaders. They may not have formal titles or leadership positions, but they understand and often shape many of their co-workers' views.
At the same time, it is important to note that a number of studies have been finding increased levels of employee anger at work. There is a wide range of causes, but one of the most common is a gap between employee expectations and employee experiences. This means that it may be helpful for management to step back and try to see if there are any major differences between what the company is practicing vs. what the company is preaching.
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