Unions and illegal immigrants

Steve Sailer ponders why the AFL-CIO seems to be in favor of amnesty for illegal immigrants:

The AFL-CIO favors a less radical version of the Karl Rove Amnesty Plan, suggesting that they view the political impact of KRAP very differently than Rove does. The unions see two benefits. First, amnesty increases the number of potential union members by bringing illegals out of the shadows. Second, by threatening to destroy American wage levels, KRAP will increase desperation among workers and make them turn to the unions for protection from guest workers, just as the unions first became hugely powerful during the Depression when the supply of labor was far greater than the demand.