Here's my fact-check of this claim:

Reasoning:

• The U.S. Justice Department did file a motion to intervene and dismiss a private citizen lawsuit brought by the NAACP and other groups against xAI and its subsidiary MZX Tech LLC, alleging violations of the Clean Air Act related to gas turbines in Southaven, Mississippi¹².
• The lawsuit alleges xAI is operating dozens of natural gas turbines without proper emissions controls and without the permits required by the Clean Air Act, creating health risks for nearby communities in Mississippi and Memphis¹³.
• The DOJ's official filing states that "the State of Mississippi — which is charged with administering the permitting program — decided no permit was required" and argues that the federal government has authority under the Clean Air Act to intervene in citizen suits, with constitutional enforcement discretion lying with the President².
• The DOJ also argues the AI data center is "critical to the economy and the Department of War" and that the lawsuit would "turn off critical power during an energy emergency and hinder the War Department's use of AI for national defense"²¹.
• While the DOJ frames its argument partly around state permitting authority and federal enforcement discretion rather than asserting an explicit standalone "legal right," the practical effect of its motion is to defend xAI's operation of the turbines without standard federal emissions permits.

Overall validity: 90%

1. Justice Department seeks to dismiss air pollution lawsuit against Musk's xAI | AP News
2. Office of Public Affairs | Justice Department Files to Intervene and Dismiss Lawsuit that Would Hamper America’s AI Innovation and Security | United States Department of Justice
3. Groups threaten lawsuit over xAI’s unpermitted gas turbines in Mississippi - Southern Environmental Law Center