If you, A) own short call option contracts; B) you receive an exercise notice prior to expiration; or C) let your short call option contracts finish in-the-money, the cost to assign each option is $20 per position.
If your short call position is assigned, you won't have to pay a separate trade cost.
Please note: Options trading involves risk and isn't suitable for every investor. Before investing in options, please read the Characteristics and Risks of Standardized Options.