Writing in today's Herald, Mr Rennie expresses his deep concern over the circumstances in which Police Scotland Chief Constable Sir Stephen House could decide that certain officers must wear sidearms at all times.
Mr Rennie says: "It was supposed to be that carrying guns was the exception. Now it is being normalised.
"Police officers are carrying guns at traffic accidents, controlling crowds outside nightclubs and attending routine duties."
He rejected Sir Stephen's description of those who have raised concerns as "almost mischievous".
The Government states that it is up to Sir Stephen to make operational decisions about the necessary and proportionate use of firearms.