[perl4ever]

Well, here is a public page (with just GME) that proves the point that they can and do apply requirements to individual stocks, anyway:

https://www.tdameritrade.com/td-ameritrade-trading-restricti...

Here's another with GME and AMC:

https://www.schwab.com/margin-updates

But there are also lots of others you never heard of, that aren't mentioned.