WASHINGTON - The US telecommunications regulator plans to fine AT&T US$100 million (S$133 million) after the telco sharply slowed down data speeds to customers of its unlimited mobile data plans.

The Federal Communications Commission (FCC) on Wednesday said AT&T misled millions of customers who subscribed to its Mobility's unlimited data services. It alleged that AT&T "severely slowed down the data speeds for customers with unlimited data plans and that (it) failed to adequately notify its customers that they could receive speeds slower than the normal network speeds AT&T advertised".

AT&T's tactics violated the 2010 Open Internet Transparency Rule by ratcheting down data transfer speeds to customers, the FCC said, adding: "Consumers deserve to get what they pay for."

AT&T, which has 30 days to contest the fine, said it would fight it, saying it extensively warned customers in 2011 that some high-volume users would see their transfer speeds slowed.

It also argued that the FCC endorsed its speed management programme several times.

"We will vigorously dispute the FCC's assertions. The FCC has specifically identified this practice as a legitimate and reasonable way to manage network resources for the benefit of all customers, and has known for years that all of the major carriers use it," the company said.

AGENCE FRANCE-PRESSE