Fig.: to be in charge and make the decisions

After a shaky beginning, the champ took the bit in his mouth and now he's the one calling the tune

Dopo un inizio traballante, il campionissimo ha preso in mano le redini del gioco ed è lui adesso a menare le danze

It's not up to you to call the tune. We have a very competent boss and it's up to him to call the shots

Non sta a te dirigere il gioco. Abbiamo un capo molto competente e spetta a lui prendere le decisioni e dare gli ordini

The full term is "Who pays the piper calls the tune", meaning whoever bears the cost of an enterprise should have authority over it (Christine Ammer: The American heritage dictionary of idioms)