A margin call refers to a broker’s call or demand to an investor (using) margin for additional securities or money. When is a margin call issued? If the equity - the difference between what you owe the broker and your securities value in your account makes a downward slide and reaches below the minimum maintenance margin, your brokerage is bound to issue a margin call. In this situation you have the option of either liquidating your position in the stock or adding more cash to the account.