A campaign group affiliated with Columbia University started a lawsuit on Friday against US President Donald Trump for continuing to block a group of users, despite a judge having previously ruled that he should no longer do this.

In 2018, another group of Twitter users went to court for the same reason. A federal court then ruled that the @realDonaldTrump account should not block accounts.

"Blocking users means that users can no longer directly interact with the president's tweets," the statement said. "In this way, freedom of expression, although modest, is actually curtailed. No more is needed to violate the constitution."

After this judgment, the President has unblocked many accounts. But the Twitter users for which the action group is now starting the case are still blocked by the president. These are users who cannot specify which tweet prompted the President to block them, and users who were blocked before the President took office.

"No new lawsuit should be needed to get the president to respect the rule of law and stop blocking people because he doesn't like what they post," said action group lawyer Katie Fallow.

The White House and Twitter have not yet responded to the lawsuit.