DETROIT, June 29 (Reuters) - The Detroit automakers and the United Auto Workers said on Tuesday fully vaccinated workers at their U.S. factories will not have to wear masks on the job beginning on July 12. General Motors Co (GM.N), Ford Motor Co (F.N), Stellantis NV (STLA.MI) and the union that represents their U.S. manufacturing workers said in a joint statement that those who have not been vaccinated will continue to wear masks at work. Other automakers operating in the United States have already begun lifting pandemic mask mandates as the number of new COVID-19 cases recedes.