The lack of interoperability makes it difficult for small and medium-sized carriers to buy access to AT&T's network when their customers travel outside the range of their own towers.
The FCC already requires that companies offer fair roaming agreements, but there is no mandate that networks have to be interoperable.
The lawmakers argued that consumers would benefit from interoperability requirements by gaining "greater choice of high-quality mobile devices at affordable prices."
The lawmakers wrote that interoperable networks would also help support the planned nationwide wireless network for first responders.
"As build-out of 4G LTE mobile broadband networks continues, the Commission should move quickly to ensure interoperability in the lower 700 MHz band," they wrote. "This will provide for a healthier wireless market to the benefit of all consumers, and will lower costs and increase access to wireless broadband services for public safety."
Tim McKone, AT&T's vice president of federal relations, said in a statement that the lawmakers failed to address the interference caused by adjacent television stations.
"That interference is the main reason there has been such little deployment to date by A Block license holders," he said. "Forcing carriers to place interfering radios in their smartphones will result in less efficient spectrum utilization and, importantly, a poor consumer experience."