Roedd Llywodraeth y DU eisoes wedi cwestiynu a oedd Bil yr Undebau Llafur (Cymru) o fewn cymhwysedd deddfwriaethol Cynulliad Cenedlaethol Cymru, ond erbyn hyn, mae’r Twrnai Cyffredinol wedi penderfynu peidio â chyfeirio’r cwestiwn ynglŷn â chymhwysedd at y Goruchaf Lys.
The UK Government had previously questioned whether the Trade Union (Wales) Bill was within the National Assembly for Wales’ legislative competence, but the Attorney General has since decided not to refer the question of competence to the Supreme Court.