CAC logon error - When user attempts to ssh into a server why is he getting prompted for a password?

Issue

• We are using single sign computer access cards for logging remotely to RHEL 5 & RHEL 6 servers. I have a new user who is using an uberthur 128 v5.5 cac card. When he attempts to ssh into a server he is getting prompted for a password. The really strange thing is he can use his cac to log into a redhat 6 workstation.