Therefore, buying on margin is mainly used for short-term investments. The brokerage firm has the right to change this at any time so you might find yourself with a demand to immediately pay off your margin debt balance with no warning or face having your portfolio liquidated. It also resulted in the suspension of margin trading for many years. Related Terms Federal Call Definition A federal call occurs when an investor’s margin account lacks sufficient equity to meet the initial margin requirement for new, or initial, purchases. Margin investing can be advantageous in cases where the investor anticipates earning a higher rate of return on the investment than what he is paying in interest on the loan. Investing for Beginners Stocks.