In early 2010, the U.S. Securities and Exchange Commission (SEC) announced the imminence of a sweeping new rule preventing brokers from offering individual customers unfiltered market access to direct access trading. Those transactions of customers who use brokers' own passes to exchanges, as well as to alternative trading systems (ATS) offering non-exchange trading, will begin to be better regulated.
This popular method of trading, which is a form of sponsored or direct market access trading (DMA), will affect many online investors and traders: according to the SEC's January 13, 2010 press release, around the time of the announcement, a goodly 38% of U.S. equities trading occured through this "naked access" arrangement.
Update 11/3/2010: On November 3, 2010, the SEC voted in favor of Rule 15c3-5, which takes effect within 60 days of being published in the Federal Register and which grants 6 months beyond that point to comply with the rule. For background on this rule, read on.