If for any reason you do not meet a margin call, the brokerage has the right to sell your securities to increase your account equity until you are above the maintenance margin. Even scarier is the fact that your broker may not be required to consult you before selling! Under most margin agreements, a firm can sell your securities without waiting for you to meet the margin call. You can't even control which stock is sold to cover the margin call.
Because of this, it is imperative that you read your brokerage's margin agreement very carefully before investing. This agreement explains the terms and conditions of the margin account, including: how interest is calculated, your responsibilities for repaying the
loan and how the securities you purchase serve as collateral for the loan.