TDA places stocks on their restricted list whenever they believe there's unusual trading or possible manipulation. Not sure why they're more aggressive than other brokers in doing this.
TDA and several other online brokers have been attacked (and will continue to be targeted) by hacker rings breaking into customer accounts to drive up selected stock prices. Shady companies have done the same thing by setting up several nominee accounts. By pumping up the trading volume from different accounts, it gives the illusion of increased interest when there's little to none.
----- "We simply attempt to be fearful when others are greedy and to be greedy only when others are fearful." -- Warren Buffett
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