Here's something I'm going to lose a lot of sleep over.
The Optional Practical Training Program is not a training program at all, it is a foreign-worker program for recent F-1 students, who have secured a degree in the States. OPT allows most new alien grads a year of authorized work, and it allows 29 months of authorized work if the degree is in one of the STEM fields of science, technology, engineering, or math. OPT is often used by exploitative employers as a preliminary to H-1B hirings.
The OPT program offers a bonus to employers of OPT workers of as much as $10,000 per worker if they hire an OPT alien rather than a citizen being paid the same salary. This is the case because OPT aliens are regarded as students (which they are not) and neither alien students nor their employers are required to pay Social Security and Medicare taxes.