MACUNGIE, Pa. (AP) — Thousands of Mack Truck workers were on strike Sunday at plants in three states, the first such walkout in decades. United Automobile Workers union members, many wearing red T-shirts and carrying signs, began picketing in the morning at the Mack Truck cab and vehicle assembly plant in Macungie, Pennsylvania, where the company says “every Mack truck built for the North American market gets its start.” Workers also walked out of plants in Middletown, Pennsylvania; Baltimore; Hagerstown, Maryland, and Jacksonville, Florida, the union said.