Federal regulators on Wednesday approved new requirements for brokerage firms aimed at curbing risks posed by their trading customers that get split-second access to markets to buy or sell stocks.

The Securities and Exchange Commission voted 5-0 at a public meeting to adopt the new rules. They effectively prohibit brokerages from providing customers with so-called "unfiltered" or "naked" access to exchanges or trading systems.

In arrangements known as sponsored access, brokerages that are approved to trade on exchanges rent out their access to them to unregulated clients such as high-frequency traders.

Those traders use mathematical models to exploit market imbalances and minute price differences. High-frequency trading is estimated to account for more than 50 percent of all U.S. stock trading.

Brokerages will be required to put in controls to reduce risk from their sponsored trading customers stemming from erroneous orders. The potential risks from electronic disruptions in trading at high speeds were showcased in the "flash crash" of May 6, when the Dow Jones industrial average dropped nearly 1,000 points in less than a half-hour.

Regulators have determined that the plunge occurred when a trading firm executed a computerized selling program in an already stressed market. The firm's trade, worth $4.1 billion, touched off a chain of events that ended with market players swiftly pulling their money from the stock market.

The new rules should help prevent erroneous orders, ensure compliance with regulations and enforce credit limits for trading orders, SEC officials said.

"This is part of our effort to address the risks associated with rapid electronic-trading strategies that have become more prevalent in recent years," SEC Chairman Mary Schapiro said before the vote. "As the events of May 6 demonstrated, the financial markets today are highly interconnected, and an event in one market can rapidly spread throughout the financial system."

The rules take effect in about two months and brokerage firms will have six months to comply.