Canada's broadcast regulator could soon find itself regulating roaming rates, just months after introducing new rules that made it more difficult for cellphone users to accidentally run up gigantic bills when using the phones out of the country.

The Canadian Radio-television and Telecommunications Commission is asking the country's cellphone providers for historical data on the fees they charge their customers for using their phones in the United States, as well as for copies of all existing contracts between Canadian and American carriers that allow them to share networks when their customers travel.

If the regulator decides the carriers are charging consumers wildly varying rates or taking advantage of their market position to limit consumer options it would launch consultations to determine whether rates should be regulated.

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"We put a cap on bill shock for Canadians," said Chris Seidl, executive director of telecommunications. "But we didn't address whether there's an issue with the actual charges."

About 18 million Canadians a year cross the U.S. border, spending an estimated $800-million a year in roaming fees. These are fees charged by the carriers, which strike agreements with local cellphone providers that give customers temporary access to another network without having to get a new cellphone while out of the country.

Many have complained that they come home to giant cellphone bills, which prompted the CRTC to set a $100 cap on additional phone charges and $50 for data unless a consumer explicitly agrees to spend more to keep using their phones.

The commission has asked the companies for data from 2007 to 2012, including the amount charged for voice and data services to customers while they were out of the country. It also wants any agreements with foreign carriers.

Rogers Communications Inc., Canada's largest wireless company, said it is "reviewing the request."

"We've received the commission's request for information and are reviewing that request now," a spokesperson said. "It's worth noting that we've recently introduced new international roaming rates, including our new $7.95/day data roaming rate to the U.S."

The CRTC said the companies must provide the information by Sept. 27.

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"The data requested will provide the commission with information on wireless roaming in order to assess its impact on the competitiveness of the Canadian wireless industry and the choices available to Canadians," the CRTC stated.