More than 30% of workers at Mercedes-Benz’s plant in Tuscaloosa, Alabama, have signed United Auto Workers authorization cards, the second transplant factory to hit the threshold, the union said on Wednesday. Obtaining 30% support is legally what workers need to be able to pursue a National Labor Relations Board election to obtain union representation with a majority vote. The UAW’s strategy calls for announcing a public campaign at a plant once it hits that threshold. It says it will demand that the company voluntarily recognize the union once 70% of workers sign online authorization cards or …