A journalist and multiple immigration legal advocates have been stopped and questioned at the US-Mexico border in recent months, a new report reveals, with at least one being questioned on their political beliefs, according to an investigative report by NBC News.

The report follows another earlier this month that US Customs and Border Patrol maintains dossiers on 59 lawyers, journalists and activists allegedly linked to the migrant caravan that arrived at the US border late last year. Some were flagged as "instigators" and "associates," Sputnik reported.

The five individuals covered by NBC on Monday weren't on the previously leaked watch list, but were nonetheless stopped while crossing the US-Mexico border and questioned for hours, all while being threatened with arrest and having their electronic devices searched.

Hector Ruiz, a staff attorney with the Santa Fe Dreamers Project who provides legal assistance to US asylum-seekers in the US and in Mexico, told NBC he was stopped while crossing the border on foot last December following dinner with friends in Ciudad Juarez, Mexico, which sits just across the border from El Paso, Texas.

The border agents, who claimed they specialized in criminal and terrorism cases, interrogated Ruiz for four hours about his political beliefs, his job and other matters.

"I was treated like a criminal. People were shouting at me," he said. "They asked me what my opinion was on the administration, just generally. And how we are doing economically."

They pressed Ruiz to unlock his phone and watched as he scrolled through his contact list, which includes many of his clients.

Two other legal workers with the Santa Fe Dreamers Project told NBC they'd been stopped in Nogales, Arizona, and a documentary journalist from Durham, North Carolina, said he was also stopped in El Paso.

Taylor Levy, a legal coordinator for the Catholic charity Annunciation House in El Paso, which provides shelter for immigrants on both sides of the border, had a similar experience on January 3. She told NBC her car was stopped in a way that suggested she had been flagged in advance as she approached the border crossing around 10:30 that night.

Like Ruiz, she was questioned for hours and pressed to unlock her electronic devices for CPB agents. She told NBC she was told she was not being detained, but "inspected," and would be arrested if she refused to cooperate. She was also denied the right to an attorney and prevented from contacting her teenage daughter.

"He also repeatedly asked me about my clients and what my clients tell me," Levy said, noting that agents demanded she give them access to her phone. "At that point I said: 'No, I'm not going to unlock my phone. I've told you I'm a legal professional, and it has confidential client information on it.'"

Levy was then released, but told NBC she hasn't crossed the border since, for fear of further harassment.

CBP told the HIll Tuesday it was "reviewing" the allegations and "if misconduct is substantiated, appropriate corrective action will be initiated." The Department of Homeland Security, of which CBP is an agency, didn't respond to requests for comment, but DHS officials have said they have no policy that targets journalists or lawyers.

"The government cannot use the pretext of the border to target and punish activists critical of its policies, lawyers providing legal representation or journalists simply doing their jobs," Esha Bhandari, a staff attorney at the American Civil Liberties Union, said Tuesday. "Whether near the border or not, it's a First Amendment violation, and there's nothing complicated about that."

The Committee to Protect Journalists (CPJ) has advised journalists crossing the border, "The US Customs and Border Protection agency (CBP) has authority to search electronic devices without warrant or probable cause. Civil liberties groups are challenging this power in court, but journalists should be aware that current practice risks exposing contacts, sourcing and reporting material contained on laptops, phones and other devices."

The group offers suggestions to reporters about how to protect their information and sources, including "asking border agents to call their media organization's legal counsel or by stating that the device is company property." However, "refusal to cooperate with CBP requests may result in continued questioning, travel delays, confiscation of equipment or, in some cases, denial of entry into the US for noncitizens."

"CBP's updated policies on electronic device searches state that agents are not allowed to intentionally access data that is exclusively stored remotely (for instance in the cloud), and should ensure wireless connectivity is disabled before a search," CPJ notes. "The policies state that agents must have reasonable suspicion and supervisory review for most ‘advanced searches,' in which agents connect a device to external equipment of the purpose of copying information or recovering encrypted or deleted files."