The SEC on Wednesday afternoon narrowly approved a rule mandating that all U.S. stock exchanges and markets develop a “consolidated audit trail.”

Audit trails currently vary among exchanges. Rule 613, approved by a 3-2 vote, requires the nation's securities exchanges and FINRA to craft a plan for creating, implementing, and operating a unified audit trail system and centralized database. The SEC has set a 270-day deadline for a proposal on how to best deploy a system that tracks trades at all stages, from order to execution.

The initiative evolved from efforts to make it easier for regulators to track trade data and determine the cause of aberrations, such as the “flash crash” that wreaked havoc on markets in 2010.

Elisse Walter and Luis Aguilar, both Democrats, voted against the proposed rule.

“Unfortunately, as currently structured, today's rule falls short of establishing the process that investors deserve,” Aguilar said. “I am concerned that the proposal fails to set appropriately specific requirements to ensure the creation of a comprehensive market surveillance system, one that will capture the whole of the capital markets – including both regulated and currently unregulated markets.”

He added that the decision to require all SROs to jointly file one plan with the Commission “assumes that all SROs will have equal weight and negotiation power, which is just not realistic.” The process could result in “a battle of size, not necessarily one of ideas” and “not all compromises represent improvement.”

In a statement, Walter said that although supportive of the broad concept, she was concerned the SEC was “adopting an overly cautious approach.”

“The rule we consider today is disappointingly weak,” she said.

“The rule simply requires that the SROs' plan take into account certain ‘considerations,' such as the source of data that will be reported to the central repository, the time in which data would be made available to regulators, the accuracy and reliability of the data reported, and the flexibility and scalability of the system,” Walters added, saying that the SEC should instead set “specific parameters.”

While Water also bemoaned the loss of a real-time reporting component to the rule, Randy Snook, executive vice president of the Securities Industry and Financial Markets Association praised the compromise.

He said next day reporting “is a more manageable and cost-effective approach to this kind of system.”