I'm speaking in a hypothetical, not something I've witnessed. I doubt anyone ever witnesses it willfully happen. All that is necessary is the incentives be in place for
1) Hiring manager to have incentive to hire quality talent at the most economical price
2) Foreign talent be more desperate than domestic talent
The effect is practically guaranteed even if there is exactly zero intent by the hiring manager or any conscious 'discrimination.' Incentives beget results and people may not ponder how they got there, and they often don't.
Unless you change (1) or (2) all the discrimination legislation, lawsuits, and 'training' in the world isn't worth the paper it is written on.
This is precisely what HR and hiring managers at FAANG companies are instructed and trained to avoid.