When nafta went into effect in 1994, what was the concern of labor leaders and environmentalists in the united states?

When NAFTA (The North American Free Trade Act) went into effect in 1994, American laborers and environmentalists had two particular concerns: American workers were concerned that American companies would move to Mexico where pay wages were significantly lower than in the United States.  American environmentalists were concerned that the act would lead to less strict environmental controls and policies and that pollution would increase as a result.