The Corporation may in its discretion levy charges, assessed on a pro rata basis, on the holders of foreign securities deposited with it: Provided, That any charge levied at the time of depositing securities with the Corporation shall not exceed one fifth of 1 per centum of the face value of such securities: Provided further, That any additional charges shall bear a close relationship to the cost of operations and negotiations including those enumerated in sections 77dd and 77ee of this title and shall not exceed 1 per centum of the face value of such securities.