I'm pretty sure about it - it's closer to "favor to multinational corporations at the expense of the American consumer."
These products already have labels on them, so there is no significant additional cost attached to the practice of labeling the country of origin. Food brought in from Mexico hasn't been raised with the same standards as food raised stateside. The result is lower (or at least 'different') quality. I have no problem with consumers having more information rather than less.
This isn't a bright issue for the GOP to spend some ofthat political capital on. They are wrong in this.
What political capital are they spending?