No, this is an obstruction of the free market (it lessens competition and drives up prices) and a violation of the Sherman Antitrust Act

“a violation of the Sherman Antitrust Act”

How is this a violation of the Sherman Antitrust Act?

I think you're confused about mega-mergers and the Sherman Antitrust Act.

The Sherman Antitrust Act is an antitrust law. Antitrust laws in the United States regulate the conduct and organization of businesses to promote competition and prevent unjustified monopolies (there are plenty of attempted mega-mergers that can be used as examples of unjustified monopolies).

"Mega mergers" are often anticompetitive in nature therefore the action of preventing mega-mergers is an action that comes as a result of antitrust laws (such as the Sherman Antitrust Act)Read more, not an action that violates antitrust laws.