A call (i.e., request) which is issued by a broker demanding a customer (whether a short seller or a party to a futures contract) to deposit additional cash or marginable securities to meet margin requirements following a decline in the balance of a margin account or futures account below a minimum maintenance level or a variation margin. In short selling, an investor would be forced either to put up more money in the margin account or to sell off some of the marginable securities. In futures, more money would be required to be deposited or some open positions would need to be closed or liquidated.