Living Streets Scotland, which works to create safe, attractive and enjoyable streets, says bus curtailment will disadvantage pedestrians.
Director Stuart Hay said: "It’s hard to see this decision being anything but detrimental to walking in the Scottish capital. Less provision for buses can only mean more and faster moving traffic in closer proximity to pedestrians. We are particularly concerned about the impacts at weekends, where the priority is to encourage people to enter and enjoy the city without driving.
"It's very surprising that a council, which has done so many positive things to promote walking and cycling, has made a decision of this nature. We will be closely monitoring conditions for pedestrians during the trial period."