Donald J. Trump, who popularized the term “fake news” and as president declared the news media “the enemy of the people,” is again clashing with journalists over press access, this time to his 2024 campaign events.

An NBC News correspondent said on Sunday that aides to Mr. Trump stopped him from covering an event in New Hampshire, where the former president was expected to make his first in-person remarks after Gov. Ron DeSantis of Florida dropped out of the race.

Vaughn Hillyard, a longtime NBC News correspondent who regularly covers Mr. Trump, had planned to attend as a pool reporter representing five major TV networks. But he told other campaign journalists that the Trump team objected to his presence.

“Your pooler was told that if he was the designated pooler by NBC News that the pool would be cut off for the day,” Mr. Hillyard wrote in an email to the rest of the pool that was obtained by The New York Times. “After affirming to the campaign that your pooler would attend the events, NBC News was informed at about 2:20 p.m. that the pool would not be allowed to travel with Trump today.”

Because candidate events often take place in cramped spaces, campaign journalists have long relied on a so-called pool system, in which one reporter attends on behalf of other news organizations. The television pool consists of ABC, CBS, CNN, Fox News and NBC, with the networks taking turns on a preset schedule. Each network selects the individual journalist who is assigned to represent the pool.

A spokesman for the Trump campaign, Steven Cheung, acknowledged that the network pool did not attend the New Hampshire event, but he said the Trump campaign does not “bar reporters based on their reporting.” Mr. Cheung said the campaign holds some events without a network pool, and noted that the pooling system for presidential candidates is less formal than the system in place for covering the president at the White House.

“We work with each other when it makes sense for both sides,” Mr. Cheung said.

NBC News declined to comment. Later on Sunday, Mr. Hillyard was allowed to attend a rally that Mr. Trump was holding at an opera house in Rochester, N.H.

The incident on Sunday echoed several episodes in Mr. Trump’s political career where he barred journalists from attending events or news conferences. In the 2016 campaign, he prohibited reporters from The Washington Post and BuzzFeed News from attending some rallies. As president, his administration revoked a CNN reporter’s press pass and barred certain journalists from some public events.

Mr. Hillyard has irritated Mr. Trump before with questions that the former president deemed impertinent. Last March, during a meeting with journalists aboard his plane, Mr. Trump grabbed Mr. Hillyard’s phone and asked that he be removed. “Get him out of here,” Mr. Trump told aides, according to audio published by Vanity Fair.

On Friday, at a separate event in New Hampshire, Mr. Hillyard repeatedly pressed Representative Elise Stefanik of New York, a close Trump ally, about Mr. Trump being found liable in a civil trial for sexually abusing the writer E. Jean Carroll.