Holding that joint employer situation exists only when "two or more employers exert significant control over the same employees . . . [where] they share or co-determine those matters governing essential terms and conditions of employment"
Finding continuity where successor retained essentially same workforce in same plant doing same jobs under same supervisor with some of the same equipment, providing similar services
Holding that employees' requests for withdrawal cards, even if such requests indicated that the employees no longer wished to be members of the union, did “not necessarily indicate that [they] no longer wish to be represented by it”