Video taken by a witness shows a forceful arrest involving U.S. Immigration and Customs Enforcement agents in Hempstead on Jan. 5.

The incident was posted by immigrant advocacy group Islip Forward.

The group says agents rammed a man’s head against a brick wall while detaining him outside Golden Farms Supermarket on Henry Street in Hempstead.

Ahmad Perez, of Islip Forward, identified the man as 35-year-old Isai Santos Caceras, of Uniondale.

“His head was slammed to a brick wall. He lost consciousness. He literally could not see a thing that was happening around him and he had no criminal record,” Perez said.

Perez said Santos Caceras did not receive medical attention for three days and is now being held at a detention facility in Maryland.

Perez, who leads the local ICE-watch group, said he has documented more than 600 ICE arrests to date and has seen changes in enforcement tactics.

“We’ve been seeing how they’ve been pulling up and showing up every day and it’s been changing,” he said.

Patrick Young, who teaches immigration law at Hofstra University, said the video appears to show the man not cooperating with agents. However, Young said the arrest may raise constitutional concerns.

“You can’t have unreasonable searches and seizures. You can’t deprive people of due process. These are not just for U.S. citizens,” Young said.

Young said he has seen an uptick in similar incidents across Long Island since November.

“It’s particularly troubling because this incident happened in Hempstead. Others have happened in Hempstead, and ICE has been concentrating in Nassau County because the Nassau County executive is cooperating with ICE,” he said.

News 12 has reached out to ICE and Nassau County Executive Bruce Blakeman for comment but has not heard back yet.