Climate policy increasingly focuses on pathways to achieving net zero greenhouse gas emissions by 2050, providing a clear standard against which to evaluate energy system planning. Examining the current and projected fuel mix of the electric power sector in the southeastern United States shows that an ongoing transition to natural gas for electricity risks locking in decades of greenhouse gas emissions at levels fundamentally incompatible with net zero goals. Furthermore, southeastern regulatory proceedings are not well designed to engage with this reality, although useful regulatory models are emerging. Natural gas will remain an important part of the southeastern fuel mix for years to come, but plans need to be laid today for its timely phaseout nonetheless. Going forward, southeastern regulators should incorporate net zero targets into their resource planning processes and require their regulated utilities to begin developing plans to achieve net zero.