This is no different than OSHA requiring hard hats on some construction sites. I don't see anything wrong with it and in my opinion, unless the farmer is hiring illegals, it would SAVE them money in workers compensation claims for injured backs.
True --- other businesses are expected to provide ergonomic equipment and safe working conditions --- why should it be so different if you hire a different set of workers --- and the illegals' health problems might not costs a dime to those who are getting rich off their cheap labor but their health ailments are certainly costing the taxpayers.