They were sent in Sept, 2012 to the TWU and affected employees:texasreb said:I never got a warn letter or have seen one and I was at AFW till the end.
https://twu514.org/blog/2012/09/page/4?print=print-page
Big thread on this website about it:
http://www.airlineforums.com/topic/54301-american-airlines-issued-warn-letters-to-the-twu-international/page-1