By Diane Bartz

WASHINGTON (Reuters) - A federal appeals court in California on Monday dismissed a U.S. government lawsuit that accused AT&T Inc <T.N> of deception for reducing internet speeds for customers with unlimited mobile data plans once their use exceeded certain levels.

The company, however, could still face a fine from the Federal Communications Commission regarding the slowdowns, also called "data throttling."

The U.S. Court of Appeals for the Ninth Circuit said it ordered a lower court to dismiss the data-throttling lawsuit, which was filed in 2014 by the Federal Trade Commission.

The FTC sued AT&T on the grounds that the No. 2 U.S. wireless carrier failed to inform consumers it would slow the speeds of heavy data users on unlimited plans. In some cases, data speeds were slowed by nearly 90 percent, the lawsuit said.

The FTC said the practice was deceptive and, as a result, barred under the Federal Trade Commission Act. AT&T argued that there was an exception for common carriers, and the appeals court agreed.

Asked about the appeals court ruling, a spokesman for AT&T said: "We're pleased with the decision."

An FTC spokesman said the agency has not yet decided whether to appeal. "We are disappointed with the ruling and are considering our options for moving forward," FTC spokesman Jay Mayfield wrote in an emailed comment.

The company, however, could face action from the FCC. In June 2015, the agency proposed a fine of $100 million for AT&T's alleged failure to inform customers with unlimited data plans about the speed reductions. AT&T has contested that proposed fine.

(Editing by Paul Simao and Matthew Lewis)