After being trained as a cashier they must be moved over to the grocery appendix scale. It is union illegal to keep them on the c.c. pay scale. According to bylaws a c.c. can not cashier. I would contact the union because they're also loosing out accruing cashiering hours.
They have to say something. Otherwise they can and will be paid at the same rate they are now. They should ask their union. Once when I was a cc and making their wage, i was asked to 'fill in' as a checker. I was "how much will my pay rate go up?" They looked at me like i had grown 2 heads and sprouted wings. "Nothing? Your wage stays the same." I politely declined. They were mad. But why should i step up and do another job which pays more than what i make? If it were for 1-2 days, I would do it no problem. But it was constantly trying to get me to do it.