BOSTON (CNN) — Commuters didn’t have to attend the protest of ICE detention facilities — the protest came to them.

Immigration advocates blocked streets and caused gridlock during the Thursday evening commute in Downtown Boston. When it was all over, police had made a dozen trespassing arrests.

The group Never Again, which organized the march, was protesting private companies doing business with Immigration and Customs Enforcement.

Hundreds of singing and chanting protesters marched at least a couple miles on the street blocking all traffic. … And it certainly grabbed attention.

“I mean it inconveniences people so it gets the message out,” one driver said.

“Sometimes you have to make a statement. That’s a statement. So, that’s good,” another commuter said.

But some drivers wondered whether it punished the public more than certain Boston companies.

“It’s rush hour, there’s only one way. Take some other way around,” one man said.

Another man expressed concern because he had to pick up his wife at the hospital. He was not alone. The proximity to Massachusetts General Hospital worried some bystanders.

In the distance, one could see the flashing lights of an ambulance momentarily stopped in traffic as the large crowd blocked an intersection.

Boston police officers who walked the route quickly worked to clear the crowd for multiple emergency vehicles that needed to pass.

Protesters refused to divulge their route to police, even as officers kept the crowd on foot and confused drivers safe.

At the end of the march, protesters sat and sang inside the Amazon office in Cambridge.