For Long Calls in both Cash and Margin accounts, options will be liquidated if they are in-the-money upon expiration and there is not enough overnight buying power in the account to support the exercise.
For Long Puts in both Cash and Margin accounts, options may not be allowed to be exercised early if the underlying shares are not held long. On the expiration date, Long Puts in Cash accounts that are in-the-money without owning the underlying shares may be liquidated. For Long Puts in Margin accounts which do not hold the underlying shares, an exercise may be allowed if the account can support the resulting position.
Level 3 Option Spread Trading is in the works. Options are a risky investment, and not suitable for all investors. Please read the Characteristics & Risks of Standardized Options before you begin trading.