A “disturbingly large” number of U.S. securities brokerages are not filing mandatory reports with regulators about customer transactions that could signal money laundering, the Securities and Exchange Commission’s enforcement head said on Wednesday.

Brokerage firms file an average of five reports each per year, a number that is “disconcerting” and “far too low” given the and industry’s volume of transactions, said Andrew Ceresney, director of the SEC Division of Enforcement, in prepared remarks.

The SEC is considering enforcement cases against brokerages whose reporting efforts fall short, Ceresney said at an anti-money laundering conference in New York.

“If and when the commission does take action, I expect it will send a strong and clear message” about the importance of complying with the law, Ceresney said.

Money laundering, or transactions aimed at hiding that the money involved was obtained through criminal acts, such as penny stock scams or terrorism, has become a major concern among regulators. A federal law requires financial institutions including brokerages to report suspicious activity, such as certain cash deposits, to regulators.

An SEC task force, which launched an analysis of so-called “suspicious activity reports” last year, found that the nearly 4800 U.S.-based securities firm file between 18,000 and 25,000 reports about suspicious transactions each year. The time period that the task force reviewed is unclear.

Some firms do not file any reports, while others file just one per year, Ceresney said. “Judging by the numbers, I find it hard to believe that the industry as a whole is fulfilling its obligations,” he said.

The SEC is still trying to sort out why firms did not file reports, Ceresney said. The agency has identified those firms and launched dozens of investigations and examinations in cases where the failure to report cannot be “easily explained,” Ceresney said.

Ceresney’s remarks follow several SEC enforcement cases.

Oppenheimer & Co, for example, agreed to pay $20 million to settle allegations by the SEC and the Treasury Department’s Financial Crimes Enforcement Network that it aided and abetted a customer’s illegal activity by selling penny stocks and ignored red flags about the customers’ transactions.