I just watched the Bug’s Bunny cartoon “Hurdy Gurdy Hare” (1950). At the end Bugs Bunny is playing a (barrel organ?) out in the street while money showers down. Bugs turns to the audience and says “I hope Petrillo doesn’t hear about this.” The reference is to James Caesar Petrillo, then leader of the American Federation of Musicians.
I knew there was union action in the early '40s (from joking references in “Fibber McGee and Molly”, for instance), but I didn’t realise there was another one in 1948.