Sen. Tom Udall (D-N.M.) has introduced draft "bill shock" legislation in the wake of the FCC's finding earlier this year that one in six mobile users have had unexpected increases in their monthly bill not caused by a change in their service plan.

The Cell Phone Bill Shock Act of 2010 would require carriers to notify customers by e-mail or text message free of charge when they have used 80 percent of their monthly limits under their current plan.

The bill also requires wireless phone companies to obtain customer consent before charging for services that are not covered by their regular monthly service plan.

"Sending an automatic text or e-mail notification to a person's phone is a simple, cost-effective solution that should not place a burden on cell phone companies and will go a long way toward reducing the pain of bill shock by customers," Udall said.

In a statement, CTIA said it was "concerned that this bill has the potential to cause customer confusion and frustration."

When the FCC's bill shock survey came out in May, CTIA argued that U.S. carriers already offer subscribers tools to monitor their usage, making legislation like Udall's proposed bill unnecessary.

The draft legislation is similar to measures already adopted by the European Union, which requires wireless operators to notify subscribers when they have reached 80 percent of their monthly data roaming services.