Credit unions can't take corporate accounts unless it's specifically written into their charter that corporations can be members. And even then, they're difficult to monitor, as every shareholder must first be a member, and must remain a member as long as the corporation's account is open. (And you guys thought we had it easy?)
So I don't know of many credit unions where the issue of withdrawal slips vs. share drafts even comes up.
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Just a lowly 1st Year Law Student ("1L"), so don't take anything I say seriously!