Final answer:
The U.S. Justice Department is suing to block a deal in a trial that started on March 21. More information is needed to identify the specific deal.
Step-by-step explanation:
The U.S. Justice Department is suing to block a deal in the trial that began March 21. Unfortunately, the given information does not specify what deal is being referred to in the question. The U.S. Justice Department's Antitrust Division is responsible for enforcing antitrust laws and ensuring fair competition in the market. It might be helpful to look up recent news articles or press releases from the U.S. Justice Department to find out more about the specific deal in question.