Google play games and unity question

I work on developing a little game on android in unity. I configured everything but when i start the game, the google play games login starts after i press the play button.. i have to mention that the play button is not connected in any way with the gpglogin script.. the gpglogin script contains a start method witch start the gpg services and an awake method that login the player. Why is the login happening when the user press the play button...and not when the game starts ? Sorry for my english...i dont know if explained myself for you to understand...if any futher informations is needed please tell me