Nick-L: I've seen this same procedure used by co's that suspect a high degree of naked shorting of their stock. By calling in all certificates the co can account for all outstanding shares and force naked shorts to fess up, (naked shorting is when a market-maker shorts a stock without delivering the shares.) Those holding a naked short position are forced to buy shares to cover their books.
If you have your shares in the brokers name, (not in your desk drawer) then you usually do not need to do anything in this situation. If you want to be sure, you should call your broker first.
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