This is the case currently pending before District Judge Keith Starrett in the Southern District of Mississippi. In a prior incarnation of the lawsuit, Judge Starrett dismissed the plaintiffs' complaint without prejudice for failing to allege sufficient facts to support their assertion of standing. The plaintiffs then re-filed their complaint, and briefing is ongoing in the district court.
You can find the plaintiffs' amended complaint (styled as their "Third Amended Petition") here.
You can find the United States's motion to dismiss in part and for jurisdictional discovery here.
You can find the plaintiffs' memorandum in response to the United States's motion to dismiss in part and for jurisdictional discovery here.
The United States's rebuttal memorandum is due July 5.