Answer: large business owners working together.
Context/history:
The Sherman Anti-Trust Act was the first measure by Congress to prohibit trusts. It was passed by Congress in 1890. A trust was when stockholders in multiple companies transferred their stock shares to a single group of trustees. Thus a whole industry area could be dominated by a single "trust" organization, destroying the free market of business competition. This was a monopolistic practice which the Sherman Anti-Trust Act ended. Thus the Sherman Anti-Trust Act directly went against the idea of those who believed business success should be based on large business owners colluding with one another.
