A consultation is fine if it goes like this: "Mexico, we're building a fence." When I put up a fence in my back yard I told my neighbor "I'm putting up a fence to keep my dogs in my yard." No further consultations were needed.
No consultation is needed because our laws are public record and Mexico will be indirectly "consulted" when the bill is signed since Mexico will read about it in the papers. No further action is required. I guess it depends on one's definition of the word "consult".