The access cards are your property (though keep in mind, I'm not a legal counsel) so you choose what you do with them.
I think my first question would be why (couched in a diplomatic manner) - just explaining it's a highly unusual request and perhaps you can be of more assistance by understanding the purpose of their request.
My highly cynical mind initially had the thought that they're trying to look for unauthorized access....
I reviewed all the SDB books and manuals I have and did not see any commentary reqarding this type of a question.
But just realize that whatever you do sets a precendent for your institution.
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My comments are absolutely no reflection of, nor influenced by, my employer - take them at your own risk.