Supporters cheer Republican vice presidential candidate Mike Pence at a campaign rally in Scranton, Pa. (John Moore/Getty Images)

Donald Trump’s campaign has denied press credentials to a number of disfavored media organizations, including The Washington Post, but on Wednesday, the campaign of his running mate, Indiana Gov. Mike Pence, went even further.

At Pence’s first public event since he was introduced as the Republican vice-presidential candidate two weeks ago, a Post reporter was barred from entering the venue after security staffers summoned local police to pat him down in a search for his cellphone.

Pence’s campaign expressed embarrassment and regret about the episode, which an official blamed on overzealous campaign volunteers.

Post reporter Jose A. DelReal sought to cover Pence’s rally at the Waukesha County Exposition Center outside Milwaukee, but he was turned down for a credential beforehand by volunteers at a press check-in table.

DelReal then tried to enter via the general-admission line, as Post reporters have done without incident since Trump last month banned the newspaper from his events. He was stopped there by a private security official who told him he couldn’t enter the building with his laptop and cellphone. When DelReal asked whether others attending the rally could enter with their cellphones, he said the unidentified official replied, “Not if they work for The Washington Post.”

After placing his computer and phone in his car, DelReal returned to the line and was detained again by security personnel, who summoned two county sheriff’s deputies. The officers patted down DelReal’s legs and torso, seeking his phone, the reporter said.

When the officers — whom DelReal identified as Deputy John Lappley and Capt. Michelle Larsuel — verified that he wasn’t carrying a phone, the reporter asked to be admitted. The security person declined. “He said, ‘I don’t want you here. You have to go,’ ” DelReal said.

The security person wouldn’t give his name when DelReal asked him to identify himself. He also denied DelReal’s request to speak to a campaign press representative as he escorted the journalist out.

Officials of the Waukesha County Sheriff’s Department were unavailable for comment Wednesday night.

Trump has banned nearly a dozen news organizations whose coverage has displeased him, but reporters have generally been able to cover his events by going through general admission lines.

The Post’s Margaret Sullivan explores what might have lead Donald Trump to revoke the newspaper’s media credentials. (Peter Stevenson/The Washington Post)

The incident involving DelReal marks another in a series of run-ins between the news media and the campaign.

In June, Politico reporter Ben Schreckinger was ejected from a Trump event in San Jose by a campaign staffer and a private security guard after he tried to cover the rally without the campaign’s permission. In February, a photojournalist from Time magazine, Christopher Morris, was roughed up by a Secret Service agent as journalists rushed to cover a protest at one of his rallies. And Trump’s former campaign manager, Corey Lewandowski, yanked and bruised the arm of a reporter for Breitbart News, Michelle Fields, when she tried to question Trump after a speech in March.

DelReal’s experience on Wednesday elicited a rebuke from Post Executive Editor Martin Baron.

“First, press credentials for The Washington Post were revoked by Donald Trump,” he said. “Now, law enforcement officers, in collusion with private security officials, subjected a reporter to bullying treatment that no ordinary citizen has to endure. All of this took place in a public facility no less. The harassment of an independent press isn’t coming to an end. It’s getting worse.”

Officials from the Pence campaign initially said they were unaware of the Waukesha incident when asked for comment Wednesday night. But after a cursory investigation, one official, who declined to speak on the record, said that no members of the campaign’s staff were involved. He said volunteers went too far.

“It sounds like they misinterpreted what they were supposed to be doing,” the official said. “This is not our policy.”

In a statement, Pence press secretary Marc Lotter said, “Our events are open to everyone, and we are looking into the alleged incident.”