Originally Posted by Blackcat31:
I think you should tell them that their payment is late and late fees will apply UNLESS they pay you cash tomorrow otherwise, late fees will continue to accrue until the money is actually AVAILABLE to you.
Bet they cough up the cash....especially since it is a nice way to avoid all those "hefty" late fees. (this is assuming you have a good late fee rate) 
This is definitely the best way to handle things. I'm a chicken though so I know it would be hard for me to say anything, but I think BC is 100% on the money!