In America, we have a concept where only the Judicial branch can interpret the laws. So, Congress passes a law, those laws sometimes give agencies like the FTC

In America, we have a concept where only the Judicial branch can interpret the laws. So, Congress passes a law, those laws sometimes give agencies like the FTC regulatory powers- but only a judge can interpret the laws to ultimately decide what those regulatory powers are. In this case, a judge will need to look at the laws passed by Congress, any relevant regulation (and if that regulation was legally authorized by Congress), and determine if this merger would violate those laws.