Goldman Sachs reported rival Wall Street bank Morgan Stanley to Hong Kong’s financial regulator over a series of block trades, according to people familiar with the matter.

Goldman alerted the territory’s Securities and Futures Commission three years ago as part of an “informal” discussion about price drops in the stocks of a small number of Hong Kong-listed companies that occurred shortly before Morgan Stanley brought blocks of shares to market, one of the people said. “It’s noteworthy to file a complaint on a competitor,” the person said.

News of the previously unreported discussion comes as Morgan Stanley faces a US federal investigation into its block trading business, where bulk sales of shares by an investment bank are typically big enough to move markets.