freeradius force authentication reject for some users?

Hi List, I am using radius based otp ubikey authentication like this: http://www.linuxforu.com/2011/08/setip-two-factor-authentication-using-openo... is there nice way to reject some users? just want to reject radius authentication for user foo. this user has account on otp, but want to reject all authentication attempts on radius? is there option to force-reject-authentication for user foo2,foo3? on freeradius? thanks, -- Eero