Once again, a nationwide AT&T outage has left customers scrambling on Tuesday.

In a statement to CNN, AT&T acknowledged a major issue preventing many of its customers from completing calls to other carriers. This problem also affects customers from other services trying to reach AT&T users.

While calls between AT&T customers are still connecting, many have taken to social media to report complete disruptions in their service. Fortunately, internet access remains unaffected.

“The carriers are working as quickly as possible to diagnose and resolve the issue,” said an AT&T spokesperson.

AT&T has not disclosed the number of affected customers, but Down Detector showed a significant increase in issue reports starting around 1 pm ET. These reports surged throughout the afternoon but began to decline by 6 pm ET. The site identified New York City, Chicago, Philadelphia, Dallas, Pittsburgh, and Indianapolis as major hotspots for these problems.

Due to this interoperability issue, thousands of Verizon customers also reported service outages on Down Detector on Tuesday.

Despite the disruptions, AT&T assured CNN that 911 calls are still going through. However, some areas like Camden County, Georgia, and Scranton, Pennsylvania, issued social media alerts about 911 call disruptions. AT&T clarified that these alerts were accidentally triggered and is investigating the error.

This outage comes less than four months after a massive disruption that crippled AT&T’s network for nearly 12 hours. In February, tens of thousands of AT&T customers across America were unable to make phone calls, send texts, reach emergency services, or access the internet due to a network outage.

Adding to the chaos, in March, AT&T reported a hack that compromised sensitive customer information, including Social Security numbers.