Consumers Union asks FCC to do more to stop mobile 'bill shock'

"The FCC should adopt a 'circuit breaker' rule that allows consumers to avoid having to pay overage fees," Riley said. "The decision to accept overage fees should rest squarely in the hands of informed consumers.”

The wireless industry has consistently maintained that "bill shock" is not as widespread as advocates claim. They have also disputed the FCC's estimate that one in five mobile subscribers has experienced an unexpected increase in their monthly bill.

In comments filed with the FCC on Monday, AT&T argues wireless carriers have significant incentives not to hit customers with overages and additional fees and that the market has largely sorted out the problem of unexpected spikes in monthly bills.

AT&T also questions whether the FCC has the legal jurisdiction to enforce bill-shock rules with regards to mobile broadband or text messages, both of which fall outside of Title II of the Telecommunications Act.

"Finally, the Commission has identified no source of statutory authority to impose any of its proposed rules on wireless broadband Internet access or SMS text-messaging services, both of which are information services outside the scope of Title II of the Communications Act. Unless the Commission can fill this jurisdictional void, it cannot adopt rules to prevent unanticipated overage charges for wireless data or SMS services," AT&T said in its filing.