Immigrants working on construction worksites were detained by federal authorities in Montgomery Thursday, advocates reported.

At least five construction workers from a D.R. Horton home building site were detained by U.S. Customs and Enforcement agents.

“It is my understanding that they were looking for a single individual and they let everyone else go at first. And then after having interactions with some people, they followed these folks and detained them on the highway,” said Luis Eduardo Robledo, an organizer from Birmingham Migra Watch.

The group formed last month to allow volunteers to monitor and publicize immigrant detentions.

Robledo said the officers arrived at the work site at about 10 a.m. and detained about five workers several hours later after they drove away from the work site.

Robledo said he does not know where those workers are currently and he does not believe the agents had warrants for their detention.

“They say they’re looking for one person, and they end up taking many more,” said Robledo.

D.R. Horton and ICE did not immediately respond to requests for comment about the detentions Friday.

The detentions reflect an increase in immigration enforcement activity both in Alabama and nationwide as the Trump administration moves forward with its effort to carry out mass deportations.

As of June 1, 51,302 immigrants were in ICE detention nationwide, according to data shared by the Syracuse University’s TRAC project, numbers not seen since the end of the Obama administration. Of those currently detained, 44% have no known criminal records.

Robledo said his group, which has set up a tip line for volunteers and immigrants to report ICE activity, also heard of detentions at several other D.R. Horton work sites in Montgomery Thursday, although he did not personally verify those reports.

On Wednesday, the group said that about 50 detainees were being held in the Homewood ICE office after the agency had detained immigrants who came in for scheduled check-ins about their cases.

On June 3, Mobile County officials arrested 28 people who were allegedly in the country illegally.