(Bloomberg) -- Regulators rejected a last-minute request from U.S. stock and options exchange operators to delay by a year the start of a far-reaching new market-surveillance system.

Exchanges are required to begin feeding trading data into the Consolidated Audit Trail on Wednesday under a U.S. Securities and Exchange Commission rule passed last year, and not complying could open them up to punishment from the regulator. After quietly lobbying for a delay, on Monday they formally asked for a one-year reprieve, citing cybersecurity concerns and other issues.

The SEC turned them down late Tuesday. In a statement, Chairman Jay Clayton said talks with the exchanges in recent days had been “constructive,” but he said he was “not in a position to support the issuance of the requested relief on the terms currently proposed.”

The system, known as the CAT, is among the biggest databases ever conceived, meant to track billions of orders a day. It’s intended to help the SEC catch manipulators and diagnose the causes of market turmoil. It was first discussed before the infamous May 2010 Flash Crash, one of the worst routs in stock market history.

A year ago, SEC commissioners led by then-Chair Mary Jo White voted unanimously to approve the system’s plan, with a Nov. 15, 2017 deadline for exchanges to begin feeding data into the system. The bourses asked to move that date to Nov. 15, 2018.

The Securities Industry and Financial Markets Association, whose members include big brokerages, had also asked the SEC to delay the system. Large brokers are supposed to start submitting information, which will include sensitive client data, in November 2018.

The attempt to stall the project comes amid heightened concerns about cybersecurity -- an issue underscored for many in the industry by the hack of Equifax Inc.’s database of credit reports and the breach of the SEC’s Edgar database of corporate filings.

Clayton also said that the SEC was evaluating whether the CAT needed to include personally identifiable information. The system as envisioned could ultimately include personal details for more than 100 million trading accounts.

“I have made it clear that the SEC will not retrieve sensitive information from the CAT unless we believe appropriate protections are in place,” Clayton said.

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