Controlling labor slugging in New York's Lower East Side, Rosenzweig's organization of around one hundred acted mostly as strikebreakers, specializing in breaking up union picket lines, demonstrations and other protests.
Rosenzweig's dominance was challenged in 1913, when Philip "Pinchey" Paul began a war with Rosenzweig, lasting over several months. The war ended with Paul's death the following year, when he was killed by Rosenzweig and several gunmen, including Jacob Heiseman, Benjamin Snyder, and Hyman Berthstein. When he was later arrested for the murder Rosenzweig agreed to testify against the other gang members. Despite his testimony Rosenzweig was sentenced to ten years imprisonment, along with Snyder, to Sing Sing Prison in December 1915.