Wind-up restrictions

[bossman72]

MLB rules. Today, had a pitcher that took 2 "rocker steps" to the side in the windup prior to stepping toward home. Hoping to be preventative, I told the catcher on the 2nd pitch of the game that he should tell the pitcher that if he does that with runners on base it will be a balk. Catcher said "he knows, obviously".

Sure enough with bases loaded, he takes 2 rocker steps and I balk it. Catcher thought I was talking about when the pitcher is in the set position when I mentioned it earlier.

My question is: did I correctly not call anything with nobody on base? Should this have been an illegal pitch and a ball?