As is pointed out in this Untouchables episode slot machines are quite legal at least at this time and the government at any level only would get involved if strong arm methods are used to put them in public places. That's when Eliot Ness and The Untouchables get involved as another would be Al Capone played by Johnny Berardino.
Berardino is trying to corner the slot machine market which is the latest mob money making enterprise. But Berardino is kind of crude in his methods. Mob attorney Theo Marcuse tells Berardino the big boys will back his play if he gets Harry Guardino to do the street work as Guardino who has just gotten out of prison has a reputation for efficiency with minimal violence. Could have fooled me with at least one of his business visits shown in the episode.
In any event Guardino just wants out and away from the rackets, but Berardino has something on him which I won't reveal.
Of course it all works out for Robert Stack and his picked crew of federal agents. Nicely done and bloodier than even the average Untouchable story.