Wall Street’s self-regulator is cracking down on abusive trades made on the basis of mathematical algorithms and currently has some 170 ongoing investigations into the subject, its chief said on Monday.

The Financial Industry Regulatory Authority (FINRA) is looking at instances in which brokerage firms may have used algorithms to engage in abusive trades, or failed to supervise the use of algorithms by their advisers, Rick Ketchum, FINRA chairman and chief executive, told reporters at the regulator’s annual conference in Washington.

Last week FINRA brought market manipulation case jointly with financial exchanges run by CBOE Holdings Inc, NASDAQ OMX Group Inc and IntercontinentalExchange Group Inc involving what they alleged was an algorithmic-trading scheme where waves of equity trades were used to artificially affect options pricing.

New York-based HAP Trading LLC and its chief executive, Harsh Padia, were ordered to give up $1.25 million in profits and pay $250,000 in penalties for manipulation and for failing to properly supervise an employee, according to a statement from the exchanges.

FINRA’s recent investigations are a response to the U.S. Securities and Exchange Commission’s 2011 so-called “market access rule” requiring brokerages with direct market access to have risk management controls and supervisory procedures in place, Ketchum said.

Ketchum’s comments come as critics such as influential author Michael Lewis, in his book “Flash Boys: A Wall Street Revolt”, accuse high-frequency traders of using their faster computers to manipulate stock prices in their favor.

FINRA is concerned about algorithms designed to trigger illegal, manipulative market behaviors such as “spoofing,” when orders are rapidly placed and canceled to create the illusion of market demand. Unsuspecting traders are then tricked into buying or selling at artificial prices, only to later find that the orders were canceled.

A large percentage of the improper market activity represents orders firms handle as agents for their clients, not necessarily market activities by the firms themselves, Ketchum said.

FINRA’s investigations have already led to some recent enforcement actions, such as the CBOE complaint filed last week, Ketchum said.

FINRA expects to announce more enforcement cases during the coming year, Ketchum said.

(Reporting by Suzanne Barlyn; Additional reporting by Emmanuel Olaoye in Washington and Tom Polansek in Chicago; Editing by Lisa Shumaker)