Get ready for the regulatory debate to heat up regarding dark pool or nonexchange trading, a practice that currently represents a third of U.S. equity trading and is generally viewed as a benefit to institutional investors seeking to minimize the impact of large block trades, and a possible uptick in trading costs.

With three dark pools or off-exchange venues in the U.S. — Pipeline, Level ATS and Liquidnet — coming under regulatory fire of late for disclosure issues, questions and concerns continue to be raised about dark pool practices and regulatory changes are expected.

That’s the finding of a new TABB Group report entitled “A Spotlight in the Dark: An Inevitable Debate.”

“Like it or not, we believe the rules surrounding off-exchange trading in U.S. equities will change; it is only a matter of time,” says Miranda Mizen, a TABB Group analyst, author of the 18-page report and a former senior vice president of transaction services at the American Stock Exchange.