If the calls you wrote go in-the-money just before ex-dividend, and you don't have the underlying stock, it is common for the calls to be exercised (the day before ex-dividend) and you will have to pay the dividend out of your own pocket as if you were short the stock! I.e. call calendar spreads, bear call credit spreads, etc. must do their research. Buying the stock to cover the next morning will be too late! Brokers do a terrible job regarding disclosure of this point, and the rule is a bit insane, because in ever other way (e.g. notice to you, margin requirements, etc.) only begins the next day. If this ever happened to you, I may have an attorney and expert witness lined up for you. You can send me a message.