A former employee of at the Seoul branch of U.S. investment bank Goldman Sachs was slapped with a fine Thursday for selling structured notes without the government's approval.

In South Korea, only registered brokerage houses can create structured notes by packaging debt with derivatives to offer customized bets, but the New York-based lender was not authorized to make such deals.

The former chief of Goldman Sachs' Seoul branch was indicted in October on charges of selling six structured notes linked to foreign currency, a deal estimated at about 600 billion won, to local brokerage houses in 2012.

The Seoul Southern District Court slapped the 50-year-old with

150 million won ($12,355), saying his act hampered "the financial market's fairness and credibility."

Another Goldman employee at the Hong Kong branch, who was involved in the deals, was fined 300 million won without a public trial.