Undeb Cenedlaethol Athrawon Cymru (Welsh, the sole official name, meaning 'National Union of Teachers of Wales') commonly referred to as UCAC, was formed in Wales from a split from the NUT in the late 40's over the issue of the Welsh language in teaching. It has around 4,000 members, who are nearly all Welsh speakers, representing mainly teachers in Welsh medium schools or teachers of Welsh in English medium schools. It accounts for about 15% of the total teacher workforce in Wales. Its main office is in Aberystwyth, Ceredigion.