追加保证金通知是指结算所或经纪行在客户的保证金水平低于最低保证金要求时，通知客户增加保证金。 A broker's demand on an investor using margin to deposit additional money or securities so that the margin account is brought up to the minimum maintenance margin. Margin calls occur when a you account value depresses to a value calculated by the broker's particular formula. This is sometimes called a "fed call" or "maintenance call". You would receive a margin call from a broker if one or more of the securities you had bought (with borrowed money) decreased in value past a certain point. You would be forced either to deposit more money in the account or to sell off some of your assets.