Having a monopoly might put you under the microscope, but you certainly can't get away with anticompetitive practices like price fixing or wage fixing even if you don't have a monopoly.
Can you link to specific examples of companies being found guilty of things like price fixing and wage fixing, where the company was not a monopoly, or part of an oligopoly?
Looks you're correct, thanks. Reading up on this a bit, I was wondering if Apple/Google/Intel/Adobe/etc constituted an oligopoly, but I don't see how that could true in this case. Also reading up on the Sherman Antitrust Act (which is what they were in violation of), the section that applied here does not require a monopoly or oligopoly.