Second, the unions made sure that employers had to pay prevailing wages to the visa holders, which makes them less attractive. And they are covered by various government regulations governing employment conditions and benefits.
I don't have a lot of sympathy for the employers. Yes, the costs will go up for their product if they pay Americans and LPRs higher wages in order to attract them to this work. The other alternative is greater mechanization and automation of the work.
Ag workers used to get paid piece work.
BTW most of the employers who hire illegals for construction are Hispanic. They pay under the table. I’ve seen them at the DMV collecting the licenses as the workers get them. I have no sympathy what-so-ever for them