I don't know the specifics of this dispute. But "terms and conditions" usually refers to the whole package, including pay, allowances, pensions, hours, tasks etc.

A change of job content (e.g. from sit at check-in desk to stand by the self-service machine) could come under a "change of terms and conditions"

Equally a pay cut would be a "change of terms and conditions".

Given sammyh's reference to single fleet, and those on current T&C's not wanting/able to fly that way, I suspect (but have no knowledge) that wholesale changes to pay structures, allowances and SOP's are proposed.