Boston’s Irish community is on high alert after ICE agents detained a local leader for deportation, sparking fears that thousands of other illegal immigrants living and working here for years could be next.

The arrest of John Cunningham — an electrical contractor and past chairman of the Gaelic Athletic Association in Boston — was particularly stunning because agents descended on his Brighton home.

Mayor Martin J. Walsh said, “This is the first time we’ve heard in Boston that somebody went to somebody’s house to take somebody. We haven’t heard that before.”

The mayor said he is seeking more information about the detainment of Cunningham, who is being held at the South Bay House of Correction.

“There’s a fear out there, we have to try and tamper the fear down,” Walsh said.

Cunningham has been detained for overstaying a 90-day visa after entering the United States in 2003, according to U.S. Immigration and Customs Enforcement spokesman Shawn Neudauer.

Irish Cultural Centre of New England President Seamus Mulligan, a friend of Cunningham’s, said the “word on the street” among Irish illegal immigrants in the region is if “someone knocks on your door at 5 a.m., keep the door closed and say, ‘Can I help you?’ And if they don’t have a search warrant, tell them to go to hell.”

Cunningham may have caught the attention of ICE when he appeared on a television show broadcast in Ireland in March and streamed online, and proclaimed his illegal immigration status in the U.S.

“All of a sudden, you turn around and too much time has gone by and you start to realize what is going to be in store for yourself for the future,” Cunningham said on the RTE Prime Time news show. “When you’re young, it’s all great. But the years go on fast and all of a sudden you end up with commitments here … a home, a job and it becomes your home.”

Mulligan told the Herald appearing on that popular program probably contributed to his friend’s downfall.

“I think that was the real reason why he was picked up, they probably figured he was a bit arrogant,” Mulligan said. “They did this as a message to send out to other people.”

Immigration lawyer John Foley, a board member of the cultural centre, said, “JC happens to be a hell of a nice guy — he’s done a lot of good for the community. When you see someone who’s done so much good taken up, that’s got to fill you with fear.”

Cunningham came to the United States through the Visa Waiver Program that allows citizens in participating countries easier travel abroad — but requires them to waive any rights to be seen by a judge if they overstay. That gives Cunningham “no recourse” against deportation now that he’s detained, according to Ronnie Millar, executive director of the Boston-based Irish International Immigrant Center.

And Millar said that many of the estimated 12,000 illegal Irish immigrants in Massachusetts have overstayed the same visa and could face similar deportation.

While deportations of Irish nationals in the Boston area have not increased from 2016 to 2017, the fear and anxiety residents have has, Millar said — and he blamed the Trump administration’s get-tough stance on illegal immigration by not just focusing on criminals exclusively.

“There definitely seems to be a shift in focus that any non-citizen is at risk of detention, regardless of their contributions or ties to communities,” Millar said. “It’s a misguided policy, there ought to be some kind of priority in terms of enforcement.”

Millar said he’s been advising nervous residents to create an emergency plan in case of sudden detainment, with guardian information for children of those detained. And he’s telling clients to demand to see a warrant before letting any officials enter their homes.