Is this a standard formula, used by other brokers too?
Margin Requirement = Stock maintenance margin requirements + 100% of in the money option value
What I do not understand is this: If I buy shares from cash (not on margin) and later sell a (covered) call on this stock and the stock price goes up, why is this considered a risk for my account and the positions are liquidated when the call is too much in the money?

Margin Requirement = Stock maintenance margin requirements + 100% of in the money option value
What I do not understand is this: If I buy shares from cash (not on margin) and later sell a (covered) call on this stock and the stock price goes up, why is this considered a risk for my account and the positions are liquidated when the call is too much in the money?