I have never heard of such a fee. Have you checked with Visa or MasterCard to see if they allow this?
If this is an allowable fee within the Visa/MasterCard rules, you will need to disclose the fee to your customers at least 30 days before you plan to start charging the fee.
On our system, a customer's card will be declined for the reason "NSF" even if their current balance is positive, but their available balance is negative (i.e. float). I'm not sure how easy it will be to explain this to your customers: "Yes, you were charged an NSF decline fee, but no your account was never negative."
I'd tread carefully and review this concept from all possible angles before attempting to implement this.
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"Gratitude makes sense of our past, brings peace for today, and creates a vision for tomorrow." - Melody Beattie