Recently I scheduled a BoA online bill payment for my Citi AAdvantage MasterCard for one day ahead of the due date.

When Citi charged me a late fee, I called and was told the ACH processing had delayed their "posting" until after the due date.

Long story short, I called BoA and their agent called Citi with me on the line, and finally got the late fee rescinded.

BoA agent told me that CitiBank had changed only their airline miles accounts to be delivered by check (which apparently was delayed by the Holidays).

Beware that Citi is playing tricks to levy late fees even for payments received on time and not waiving delays caused by ACH processing.