Amid the uncertainty over net neutrality’s future, AT&T said earlier this week that it was halting investments into its high-speed fiber network. Challenging the telecommunication company, the Federal Communications Commission shot back Friday with a letter demanding proof that fiber would be an unprofitable business for AT&T under net neutrality.

On Monday, President Obama publicly came out in support of net neutrality, calling for the FCC to classify the Internet as a utility and impose more stringent regulations on Internet service providers. Clearly unhappy with the news, AT&T CEO Randall Stephenson quickly responded by saying the provider would pull back on the proposed rollout of its fiber network in 100 cities. “We can’t go out and invest that kind of money deploying fiber to 100 cities not knowing under what rules those investments will be governed,” he told investors.

The letter from the FCC requests documents showing AT&T’s plans for fiber deployment, including the number of households affected before and after it announced the decision to pause its investments. In addition, AT&T is asked to explain why “fiber deployment is now unprofitable,” and whether its acquisition of DirecTV, expected to close in the second quarter of 2015, would make such deployment unprofitable.

AT&T has until November 21 to respond.