You could also use:  public mouthpiece
 
 
Examples:
The media is a government mouthpiece, not a government watchdog. 
 
are they the public mouthpiece for the bureau of.. 
 
The Chamber Of Commerce suddenly found it had a public mouthpiece in The Guardian as the Smedley brothers � printing press rolled out the weekly
 
Mouthpiece for the public sounds better than of the public in your example, (to me) and I believe it is more usual. However, I have seen mouthpiece of the government  used also.