Auto-exercise, or Exercise By Exception as it is often referred, is a clearinghouse process intended to ease the operational burden of clearing members having to inform the clearinghouse as to which options to exercise. In the case of securities options, OCC has a threshold by which all options which are in-the-money by at least $0.01 or more are exercised unless contrary instructions are provided by the broker.
The decision as to whether to allow a client to exercise an option without having the financial capacity to carry the underlying upon delivery is broker specific. However, consistent with the policy of not issuing margin calls, IB generally does not allow clients to exercise options if, after giving effect to the exercise, the client's account would not be in margin compliance.
As an extreme example of why this is not allowed, consider an account with nominal equity purchasing an at-the-money call option which is paid for in full and therefore requires no margin. Using GOOG as an example, the $540 weekly call option expiring tomorrow (Sept 2, 2011 ) closed today at $1.30, with the stock at $541.01. An account holding only $1,000 in cash could theoretically buy 5 of these call options and, were the final settlement price of the stock to end at $540.01 or more at expiration, be subject to the delivery of stock valued at approximately $270,000 with virtually no assets to meet the ensuing margin requirement. Were that exercise to be allowed, the stock would be liquidated upon the open given the margin deficiency, however, it's easy to see the uncollateralized exposure the broker is subject to if that stock opens down relative to the strike price.
To minimize exercise-related exposure, IB may take any one of the following actions at expiration:
1. Close out positions on the last day of trading;
2. Restrict the account to closing trades only;
3. Lapse (disallow exercise) some or all of the long contracts which are in-the-money; and/or
4. Immediately liquidate underlying positions subject to delivery effective with the option expiration.
As a general rule, you will receive an email/bulletin advising you if a review of your account indicates post-expiration exposure which exceeds your financial capacity. These notices are typically sent as early as 2-3 hours prior to the close, although it should be noted that advance notice cannot always be assured, particularly in those situations where the exposure does not surface until near or at the close as positions and prices change.