The NYT has a really good (except for the title) article on undocumented day worker organizing conference at Hofstra University on Long Island.

As delegates from 29 worker organizations in 12 states shared
successful tactics and tales of persecution in small groups, some having driven
all night to make the meeting, Mr. Alvarado stressed that many towns had tried
and failed to disperse day laborers through aggressive law enforcement.
"They
send police on horses, police on bikes, and they give tickets for jaywalking,
trespassing, littering, loitering," he said. Even helicopters have been used to
chase laborers, he added, citing practices in Algura Hills, Calif., where he
said undercover cops posing as contractors have been known to transport workers
to out-of-the-way places and leave them to walk back.