If you are referring to national immigration quotas then I agree that yes, it was quite unfair for awhile now.
It's just a bit odd. There wasn't even a hard physical border with Mexico until the 1920's. There used to be a rather active workable "temporary farm worker visa" program that got sacrificed on the altar of pleasing xenophobic morons somewhere in the 70's or 80's I guess...
As a person that lived thru it, it was not xenophobia, it was NAFTA that sent everyone scrambling to survive. Our farm lost viability due to it, as did most small family farms. You either conglomerated with the emerging mega-farms if you where big enough or you died. Organic was nowhere on the horizon at that time and was the only thing that brought back the viability of small plot farming. Xenophobia is an easy answer to reach for, but the reality is people where scrambling to save their livelihoods and kicking the legs out from under the big conglomerates via removing the migrant workforce they relied on was one of the efforts. It has more to do with surviving than a disdain for other people. Also there was no love loss for the big conglomerates as they where the very entities that pushed for NAFTA, so trying to remove their workforce was fair game.
In the end I miss the family homestead but it worked out for me. I was a crappy citrus farmer (due to lack of passion) and while I appreciate my youth, I don't ever want to own a farm so I am glad my family got to reap the rewards of selling it, rather than me inheriting a farm that I would have to figure out what to do with.
The visas in question made it easy to legally hire foreign (mostly Mexican, I’d guess) agricultural workers. That would have reduced the cost of farming your family homestead.
Canceling the visas presumably encouraged many of those workers to accept lower wages to work farms in Mexico. The old visa program was effectively a subsidy for US farms; ending it created more competition for US farms. Arguably, it also made NAFTA more likely to happen, since it moved agricultural production from the US to Mexico, and people have to eat.
Suspending the H-1B and green card programs will have the same long term effect on the US tech industry.