The Justice Department is investigating the five major US news networks for possible antitrust violations, opening yet another front in the Trump administration's pressure campaign against the press. The probe, which one leading First Amendment group called nonsensical, concerns the TV pool, a long-standing arrangement that was disrupted last month when President Donald Trump banned CNN from the White House grounds. The pool is a small, rotating group of journalists that provides coverage of the president and represents the larger press corps. There was no pooled TV coverage of Trump's events for several days until a federal judge issued an order temporarily halting Trump's ban on CNN, MSNOW and Politico. That litigation is ongoing, and the Justice Department is defending Trump's action in court. Now, the Justice Department is also probing how the TV pool functions. The highly unusual inquiry was first reported by The New York Times on Saturday. In a statement to CNN, a Justice Department spokesperson confirmed the contours of the investigation. "Members of the television press pool have boycotted covering White House events. Group boycotts among commercial competitors can violate the Sherman Act," the spokesperson said. Representatives for the five networks that have made up the pool for decades — ABC, CBS, CNN, Fox News and NBC — either declined to comment or did not respond to requests for comment on Saturday night. 📸: Daniel Heuer/Bloomberg/Getty Images/File - @cnn