CNN  —  A nationwide AT&T outage is once again leaving customers in the dark on Tuesday. In a statement sent to CNN, the company said a glitch is preventing AT&T customers from completing calls between carriers. Calls between AT&T customers aren’t impacted. “The carriers are working as quickly as possible to diagnose and resolve the issue,” a company spokesperson said. Although the company did not share the number of impacted customers, website Down Detector shows a spike in reports of issues using the service starting around 1:00 p.m. ET. Those numbers climbed in the hours that followed. The site lists New York City, Chicago, Philadelphia, Dallas, Pittsburgh and Indianapolis as among the cities with the most reports of issues. AT&T told CNN that 911 is not impacted at this time.