You need to look at your contract with VISA/MC that you entered into when you began processing cash advances - Everyone of them that I have seen require you to process cash advances for any consumer holding their (VISA/MC) logoed card and further, they have always forbid the FI from charging a fee for process the cash advance. There is generally a maximum cash advance amount that you must process to (ours is also $5k) but you can certainly process higher amounts.
I would recommend either finding your contract, or contacting your processing rep.
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My comments are absolutely no reflection of, nor influenced by, my employer - take them at your own risk.