▁articles ▁ 3 9 ▁and ▁ 4 0 ▁of ▁the ▁Constitution ▁dealing ▁with ▁the ▁freedom ▁of ▁trade ▁union ▁organisation . ▁ ▁When ▁the ▁Part ito ▁d ’ A zione ▁dissol ved ▁in ▁ 1 9 4 7 , ▁F oa ▁joined ▁the ▁Part ito ▁Social ista ▁Ital iano ▁( Ital ian ▁Social ist ▁Party , ▁P SI ) ▁and ▁was ▁elected ▁an ▁MP ▁in ▁ 1 9 5 3 ▁( and ▁again ▁in ▁ 1 9 5 8 ▁and ▁ 1 9 6 3 ). ▁In ▁ 1 9 5 7 , ▁he ▁joined ▁the ▁left - wing ▁trade ▁union ▁of ▁Giuseppe ▁Di ▁Vitt orio , ▁the ▁CG IL , ▁and ▁became ▁an ▁influ ential ▁and ▁highly ▁char ism atic ▁trade ▁union ▁leader . ▁ ▁A ▁leading ▁intellectual ▁of ▁the ▁Italian ▁non - Comm un ist ▁left , ▁F oa ▁supported ▁the ▁theory ▁of ▁the ▁political ▁aut onomy ▁of ▁the ▁working ▁class , ▁which ▁would ▁later ▁insp ire ▁the ▁foundation ▁of ▁extra - par liament ary ▁left ist ▁groups ▁( P SI UP , ▁P d UP , ▁D P ). ▁ ▁At ▁the ▁end ▁of ▁the ▁ 1 9 7 0 s , ▁F oa ▁left ▁the ▁trade ▁union ▁and ▁active ▁political ▁life ▁to ▁dev ote ▁himself ▁to ▁historical ▁research ▁and ▁publishing . ▁He ▁taught ▁Modern ▁History ▁at ▁the ▁Univers ities ▁of ▁Mod ena ▁and ▁Tur in ▁and ▁research ed ▁the ▁history ▁of ▁the ▁working ▁class ▁and ▁of ▁the ▁trade ▁un ions . ▁Publications ▁of ▁this ▁period ▁include ▁La ▁Ger usalem me