At there place of employment? Nope, they are not established workers with SS cards, they are off the books.
At there place of residence? Nope, most likely the one who was a citizen held the lease, the others just flying under the radar.
They should offer them to chance to become naturalized, if they refuse, deport them. If they opt to, give them the resources to do so.
Other than that, I have no problem with them taking them into custody no matter where they are. Especially if it's at the welfare office with their anchor baby sucking up the food stamps, medicaid and cash assistance.