Labor unions do seem to be further to the left these days on a lot of issues. I think that part of this is also that an increasing proportion of the union movement, as opposed to the AFL-CIO specifically, is in the public sector. Teachers are not worried about losing their jobs to immigrants, nor is your average government worker.
They don't care about US workers having lower wages,what they are looking at are millions of new dues-paying union members. These people will make the unions themselves richer and more powerful,even if wages go down.