Businesses opposed the creation of labor unions largely out of self-interest. If unions were allowed to exist and gain strength, they could force businesses to give higher pay and better conditions (which also meant higher costs) to their workers.
The opposition of the middle class was based largely on their impressions of the unions. They tended to see workers as coming from a lower class of people. They did not like the idea of these lower classes gaining more power. In some cases, they were also ideologically committed to the ideas of Social Darwinism, which held that labor unions were simply ways to allow those who were less "fit" to overcome those who were fit and out to be allowed to control society and the economy.