Dark pools could be about to become a little less so.
In the coming months, exchanges that operate outside public view likely at least will have to disclose trading volume, under a draft rule the Financial Industry Regulatory Authority will be submitting to the Securities and Exchange Commission in the next month or so.
The rule will call for a rundown of how much business dark pools are doing and would provide the first look into how much activity is directed to the exchanges, according to a Traders magazine report.
A draft is expected to be submitted in October or November, followed by a comment period. Adoption would come in early 2014.
(Read more: Post-'flash freeze' sentiment is 'get used to it')
Trading firms have been reluctant allies in the cause for more transparency in the off-exchange trading world.
Credit Suisse had been reporting activity in a voluntary basis but stopped in April after it became frustrated over the lack of uniform rules and full industry cooperation.
"This regulation will get passed," Christopher Nagy, head of KOR Trading, told Traders. "The feeling of some operators is this type of mandate to report is OK but the frequency of said reports needs to be sorted out first."
This looks like a period of big changes ahead for dark pools.
(Read more: Can regulators evercontrol robot traders?)
In a little-noticed development outside its home country, the Australian Securities and Investments Commission is on its way to adopting new rules that will require investment banks to disclose information about their own dark-pool activities, and to report suspicious behavior.
Those rules could serve as a template for the way global dark exchanges work.
That's important, because the dark pools have getting more volume than the New York Stock Exchange.
—By CNBC's Jeff Cox. Follow him on Twitter.