There is no specific law against it. Just like there is no specific law against getting "protection fees" from all the businesses in the neighborhood because it would be a shame if something were to happen to it. Which is why we have racketeering/Rico laws.
Generally, when anti-trust cases go to court, they will use individual cases like these of anti-conpetitive behavior as evidence to build a case of a pattern of that type of behavior.
Generally, when anti-trust cases go to court, they will use individual cases like these of anti-conpetitive behavior as evidence to build a case of a pattern of that type of behavior.