A sampling of the kinds of books to look for. Search Catalyst for these. Try a lot of different search terms like food workers, food labor, migrant labor, farmworkers, migrant agricultural labor, and so on.

Workers, the labor movement, and food production intersects in many ways.  Wikipedia has a good list of trade unions that can lead you to additional websites of unions to research.  You can research unions both through their own documentation and also articles about them from outside sources: articles from library databases and books in library (suggested on the left).