Originally Posted by
baliktad
For the purposes of bag fees, the marketing or codeshare flight number does not matter. Only the operating carrier matters.
Actually, there's a DOT guidance letter that repudiates this in international codeshare service. If the OP has an AA-coded ticket on an international journey, the AA contract of carriage applies.
http://airconsumer.dot.gov/rules/webnotice_04012009.pdf
(I'm an AA flyer but haven't studied the C of C to see if the OneWorld luggage allowance is in the C of C, or is instead listed as a frequent flyer program benefit.)
Try to get the fees waived upon check in. If that fails, keep the receipts and send a request for refund to AA, copying the U.S. Depart of Transportation. I suspect you will receive a refund.
http://airconsumer.ost.dot.gov/CP_AirlineService.htm