I would not call the unions free marketeers and they are NOT weighing in why?"
Unions no longer represent worker's interests, but are now run by leftist ideologues. Ask "what do the leftists want?" to figure out the new union position.
leftists want 'clients' for the socialist welfare state, and voters to vote socialist, and no better clients than Mexico's exports of poverty-stricken residents looking for work and handouts. Hence, they line up for amnesty, even if it hurts American workers to have a flood of low-wage competition.
What you say about the Unions is correct. However, why have they stayed so silent about these millions of 'workers' who apparently are not under their control?
Their lack of public face is most interesting, considering they are very much for legalizing the illegal workers.
Where are they making up the short fall of income?
Look what the liberals did to attempt to disgrace the Republicans into supporting the legalization of illegals, they wrapped it into a religious dress of Republicans making Jesus illegal.
Divide and conquer and there has to be a pay off for the Unions.