A method and system for controlling application of split-uplink mode for dual-connectivity service in a system where a first access node provides service on a first air interface and a second access node provides service on a second air interface, and where (i) in a single-connection-uplink mode for the dual-connectivity service, uplink user-plane communication is carried on just the second air interface and (ii) in the split-uplink mode for the dual-connectivity service, uplink user-plane communication is split between the first air interface and the second air interface. An example method includes detecting at least a predefined threshold high level of uplink voice muting on the first air interface and responsively restricting application of the split-uplink mode for the dual-connectivity service.