All depends on what the letter said. Did it even propose a violation which may now be pending?
You may be assured that because it was issued by CBP, it will show up when CBP runs your background for GE.
I would answer the question truthfully and then bring a copy of the letter with me. If the issue arises, either directly or even in a general way, e.g. "is there anything else you want to say," you can provide the full facts and a copy of the letter.