New York(CNN) The Justice Department and a group of Twitter users faced off Tuesday in the appeal of a case over whether President Donald Trump's blocking of certain accounts violates the First Amendment.

Before a three-judge panel in Manhattan federal court, the Justice Department argued that Trump wasn't "wielding the power" of the federal government when he blocked certain individuals from his personal Twitter account, @realDonaldTrump, because while the President sends tweets in his official capacity, he blocks users as a personal matter.

But an attorney for the Knight First Amendment Institute -- which, along with seven individuals who have been blocked by the President on Twitter, sued Trump last year -- said the President's actions were taken in his official government capacity.

Though conceding that Trump had launched the account before he took office, the attorney, Jameel Jaffer, said Trump "began using it as President as an extension of his office."

Though the panel didn't rule on the matter, the judges appeared to question the Justice Department's argument. If Trump blocked people in his personal capacity, "it is curious to me that the Justice Department is here representing him," Judge Peter Hall said in response to the government's attorney, Jennifer Utrecht.

"Your very presence here represents that this" -- an apparent reference to Twitter -- "is a public forum," Hall added.

Utrecht said the department was representing the President because Trump had been sued in his official capacity.

Last year, a New York federal judge ruled that Trump had violated the Constitution when he blocked Twitter users.

US District Judge Naomi Reice Buchwald wrote in her ruling that "no government official -- including the President -- is above the law, and all government officials are presumed to follow the law as has been declared."

"We hold that portions of the @realDonaldTrump account -- the 'interactive space' where Twitter users may directly engage with the content of the President's tweets -- are properly analyzed under the 'public forum' doctrines set forth by the Supreme Court, that such space is a designated public forum, and that the blocking of the plaintiffs based on their political speech constitutes viewpoint discrimination that violates the First Amendment," Buchwald wrote.

On Tuesday, Utrecht argued that though Trump tweets in his official capacity, he blocks users as a personal matter. Judge Christopher Droney listed recent tweets by the President, including one that revoked sanctions on North Korea, another concerning the Golan Heights territory and a third on the Federal Reserve Board.

"Those aren't official actions?" the judge asked.

Utrecht said they were, but later said: "The President, when he blocks individuals from his personal Twitter account ... is doing so in his personal capacity." That prompted one judge to ask if Trump himself, rather than a personal aide or government staffer, is "entering the blocks." Utrecht replied that he is, an admission the government had also made in a stipulation.

In his argument, Jaffer warned of a slippery slope if the court were to find that Trump could block certain users while occupying the White House.

Raising the notion of a President preventing certain commenters from posting on a government website, Jaffer said, "I think you would be opening the door to the distortion and manipulation of those types of spaces as well if you were to accept this argument."

"The whole point of Twitter is to facilitate interaction among users," he said. "If the government had wanted one-way action, it could have used a blog" or another platform for Trump's comments.