Take a look at this article: Union, immigration ties concern some
A few years ago, unions viewed immigrant workers as competition to their members. Immigrant workers undermined local wage markets because they would often work for less than the locals.
Private sector workers, however, no longer need unions as much as they have in the past. Therefore, they are, by and large, unwilling to voluntarily join unions (private sector union density hangs just above 7 percent.). Realizing that they have lost their grasp on today’s workers because today’s workers do not have the same needs as their grandparents, unions are going after a constituency that has needs they can meet; illegal aliens.
Plainly speaking, unions are taking advantage of these helpless people. They are hijacking their emotive plight for political gain and they are taping into their paychecks to fill their coffers.