Pickoff from windup position???

[ElPanadero]

I thought I read something about this subject in this forum, but I can't find it.

Can you or can you not pickoff from the windup position? In other words: the pitcher has both feet on the rubber, glove and ball in front of his body, he steps directly towards 1st base with his left foot (RHP) and throws to 1B. His pivot foot still on rubber. Picks off runner.

Is this legal? Is it a balk? Anybody???