The Financial Markets Authority (FMA) has taken legal action against Mark Warminger - a trader employed by Milford Asset Management - over claims of market manipulation.
The capital markets watchdog claims Mr Warminger traded in securities that created a false or misleading appearance, breaching the Securities Markets Act.
The authority alleges the trading, which took place between December 2013 and August 2014, fell into the following categories:
The authority is seeking financial penalties against Mr Warminger in the action filed in the High Court.
The counsel acting for Mr Warminger, Marc Corlett, said his client denied that he manipulated any market and would defend the case.
Mr Warminger is on extended leave from Milford Asset Management.
Milford Asset has already paid $1.5 million following an investigation by the authority, and has undertaken to implement changes to its internal systems and controls.