Green’s Dictionary of Slang

(US) a campaigner against the power of monopolistic industrial or business trusts; thus trust-busting n.

1903		Chicago Chronicle 11 Apr. 2: Mr. Knox is surprising everybody by his zeal as a trust-buster [DA].
1944		Chicago Daily News 8 May 10/1: So we have a faint revival of ‘trust busting’ to give color to the stuff [DA].
1949		Time 9 May 34/3: U.S. trustbusters were still locked in stalemate with the Zaibatsu [DA].