Massachusetts on Thursday fined Citigroup $30 million for improperly releasing market-sensitive information on an Apple supplier to large clients including hedge fund SAC Capital Advisors.

In December 2012 Taiwan-based Citigroup Global Markets analyst Kevin Chang divulged to a handful of clients a lowered production forecast for Apple iPhones and iPads made by supplier Hon Hai a day before the research was published, the state said.

The publication of the revised forecast suggesting lower demand for Apple products helped to propel a 5.2 percent drop in Apple's share price over a two-day period.

Massachusetts alleged that SAC Capital; Citadel, another hedge fund; and T. Rowe Price sold Apple stock after receiving the information and before it was released to the public. A fourth firm, hedge fund GLG Partners, also received the early tip-off.

Chang disclosed the information to three units of SAC, the investment house of billionaire Steven Cohen which is already facing a US Justice Department criminal indictment over numerous alleged insider trading violations.

The fine came on the heels of two earlier settlements between the Citi unit and Massachusetts for similar securities laws violations.

"It seems that the concept that investors are to be presented with a level playing field when it comes to the product of research analysts is a lesson that must be learned over and over again," Massachusetts state Secretary William Galvin said in a statement.

"But it's important that it should be taught as often as necessary."

Citigroup agreed to pay the fine to close the case.

"We take our regulatory compliance requirements very seriously and train all of our employees about these obligations," Citigroup said in a statement. "We are also constantly working to improve, manage and monitor the compliance and controls process."

Chang was terminated from Citigroup in September, the Massachusetts settlement document said.