The United Auto Workers said it’s moving forward with attempts to unionize a joint-venture battery cell plant after pushback from Ultium Cells LLC, a company General Motors Co. and partner LG Energy Solution own. UAW-GM leadership attempted to establish a card-check agreement with Ultium Cells that would give the union access to the facility to collect cards as a way to organize the plant, UAW Vice President Terry Dittes told local leaders in a letter Tuesday obtained by The Detroit News. “If the majority is established by an independent third party, the union would be recognized and negotiati…