It's not a fee that has to be disclosed under TISA. I'd check to see what your standard notice practice is at the CU regarding other non-TISA matters.
My guess is that a small minority of your membership would be affected by a wire transfer fee. You could try putting a short message on statements, rather than go to the expense of mailing a notice or using statement stuffers.
John S. Burnett
Fighting for Compliance since 1976
Bankers' Threads User #8