If you have access to data that shows big tech is preferentially hiring visa holders over US citizens you should get on that class action lawsuit right away. That's probably hundreds of thousands or even millions per person in lost wages, and even after lawyers take their 30% cut, that's still a sizable chunk.

It's anecdata, but a college friend who now works at as a manager in an IT/Data consultancy in my birth country in the EU told me bluntly that they prioritized hiring foreigners as they were 20% cheaper.

Given that the company sponsors them and come from lower incomes countries, they are ready to accept lower wages. If they do it I don't see why everyone wouldn't be doing the same.

It's of course hard to prove formally as those companies will comply with regs to make it look like they aren't discriminating (fake job ads, etc...). By the way in the US Indian consultancies got busted for this.