The FCC said stock purchases of América Móvil by its billionaire owner Carlos Slim and his family repeatedly exceeded the foreign ownership levels approved by the agency. The companies have agreed to adopt compliance plans to prevent future stock purchases by the Slim family that would exceed foreign ownership limits without first receiving FCC approval.

The FCC said the amount of the fine, the largest ever for a violation of foreign ownership and control limits, was because of the Slim family’s repeated violations.

"Foreign companies doing business in the United States and its territories must follow all federal rules, including those governing their ownership of American companies," said FCC enforcement bureau chief Travis LeBlanc.

"The FCC ensures that foreign ownership in American telecommunications carriers is in the public interest, considering issues related to competition, national security, law enforcement, foreign policy, and trade policy."

The FCC said the firms have exceeded their approved foreign ownership three times in five years.

In June 2014, the Slim family increased its control of América Móvil through a purchase of stock from AT&T International, the FCC said, which increased the family’s ownership in PRTC beyond the voting and equity interests approved by the FCC.

(Reporting by David Shepardson; Editing by G Crosse and Matthew Lewis)