This is sadly less Dr. Evil than it sounds like. They're using so-called "hail cannons" which attempt to prevent hail from forming in overhead thunderstorms and generally are believed not to work by meteorologists. They're quite popular with French wine-country grape farmers in spite of that though.
From what I read in the news, the major scandal in Mexico is the fact that the hail cannons were running
even when there wasn't hail and they weren't needed, which greatly affected the weather cycles in the region, leading to a lot of negative consequences for farmers in the region. Also the area of affect for the hail cannons was much larger than simply the plant's area, another major point of contention with the Mexican locals. The farmers (and the local region itself) had no say in how the hail cannons were being operated.
This is on top of things that maiaramdan mentioned that I wasn't aware of, such as VW doing emissions testing on humans and animals, and stock manipulation.