I think this is a game changer. If they don't reverse the rule, I will be transferring my account to a prime broker. I have a material account with them and can't operate without margin. I'm not a day trader but focus on micro caps and hedge accordingly with ETFs.
I'm not sure we will see big moves in stocks as a result of this, however. I could be wrong but I'd think this only effects a small minority of their customer base.
It's a terrible business decision. They are assuming a $150 million market cap is inherently risky (or more risky) due to it's size. This is simply wrong. They might as well limit margin on all stocks with the letter "A" in the ticker. I truly believe that the people in risk management at IB and most large brokers have never managed money before and have no real idea what they are doing. For them, they'd rather save $50,000 on losses if it means costing them $20,000,000 in revenues.
I don't have a name of a retail brokerage firm that is anywhere nearly as good as IB but if your account is large enough there are many small prime brokers that would take you. If you are not big enough you might be shit out of luck.
The whole situation is awful. I just registered to post here.