Growers must replace H-2A workers with any U.S. worker who applies for the job before half of the season is over.
Growers do not have to replace their H- 2 A workers. 
mnli hypothesis: Growers do not have to replace their H- 2 A workers.  premise: Growers must replace H-2A workers with any U.S. worker who applies for the job before half of the season is over.