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An order by a brokerage for an account holder to deposit more cash or securities into a margin account when the value of the cash and securities currently in it falls below some defined percentage. Every margin account has a maintenance margin requirement, which is money or securities an investor must keep in his/her margin account in order to be able to borrow from the brokerage. FINRA requires that the maintenance margin must be at least 25% of the amount borrowed, while some brokerages require a maintenance margin of up to 50%. If the maintenance margin falls below this, the account may be subject to a margin call. If the account holder is unable to make the necessary deposit, he/she must close out enough positions in order to make the deposit, or risk the account becoming blocked.