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.

Why were the middle class hostile to workers organizing?

First, the term "middle class" must be specified, because it has meant different things at different times. During the early years of the Industrial Revolution, the term meant something like "bourgeoisie": the people who owned and profited from the means of production as opposed to working class people or titled nobility. Later, it took on a different meaning, and indeed many members of the middle class by the twentieth century were themselves union members. Business owners were opposed to the organization of workers because they felt unions took away their right to run and to profit from their businesses in any way they pleased. Unions also raised costs for business owners by demanding higher wages, better working conditions, and so on. So as the Industrial Revolution emerged, middle classes--the people who owned businesses, were opposed to unions. Later, as the term middle classes came to be associated more with income and lifestyle, many middle class people joined unions. But some middle class people, even those who did not own their own businesses, were still uneasy about unions. In many cases, this had to do with the success of wealthy Americans in associating unions with radicalism, especially early in the twentieth century.