Please be advised of the fact that Korean Air has changed the booking class for the Korean domestic flight.  Accordingly the booking class which can be upgraded will be changed as follows:  

This change will be effective as of November 1st, 2015, (Based on date of the bonus issuance)

Upgrade award change details
Until October 31, 2015 From  November 1, 2015
J, C, Y, B, M, W Korean Domestic Y,W,M Reference 1 International J,C,Y,B,M

M Reference 1  class can be applied only to KE1401~KE1410