Multiple people are reporting that they got emails from AMEX notifying them that they will be charged back for using the 10% back at Staples on multiple cards:
AMEX has been cracking down on the ability to register multiple cards for an AMEX Offer, but this is the first time that there have been clawbacks of credits due to it being used on multiple registered cards. Ouch!
So far it just appears to be targeting the Staples offer, though it’s likely to affect other offers as well in the future. It’s the end of an era for AMEX Offers.