"A Piece of the Action" began as a one-sentence synopsis from the original “Star Trek is…” proposal by Gene Roddenberry. “President Capone” was described as “A parallel world, Chicago ten years after Al Capone won and imposed gangland statutes upon the nation.” Writer George Clayton Johnson developed an outline based on this summary called “The Syndicate,” and Roddenberry liked that enough to write a treatment entitled “Chicago II.”
"Chicago II" got shelved after Johnson found himself busy writing and developing "The Man Trap," but second season producer Gene L. Coon discovered the treatment. Coon thought it would be a nice followup to "The Trouble With Tribbles," especially as he believed the series needed more comedic episodes. He worked with David P. Harmon on a first draft of what was then called "Mission Into Chaos," which featured the Romulan agents attempting to manipulate Bela Oxymyx and the other crime bosses and Kirk and crew’s fight against them in an effort to bring the planet into the Federation.