Yes, it is enforceable if both the illegal and the farmers are punished when breaking the law.Do you actually think this is enforceable?
In fact, something similar already exists in the US for retail workers during the holiday season or tourist rush.
"ORCA Seasonal Passport
Do you employ seasonal workers? Metro's Business Programs is excited to introduce our ORCA Seasonal Passport pilot program! This new transit pass is an affordable way to attract interns, seasonal, and temporary workers in a competitive job market. Whether you're hiring for the holiday season or the tourist rush, the ORCA Seasonal Passport can help you recruit the employees you need."They can transport them from the border right to the farms, and then transport them right back.