Regulators are taking steps to loosen the control that big U.S. exchanges exert over the flow of real-time stock prices to the public in an effort to lower costs for investors.

Regulators are taking steps to loosen the control that big U.S. exchanges exert over the flow of real-time stock prices to the public in an effort to lower costs for investors.

A proposal advanced Wednesday by the Securities and Exchange Commission takes aim at a two-tier system that allows trading platforms such as the New York Stock Exchange and Nasdaq Inc. to charge their largest customers higher fees for faster proprietary feeds, leaving smaller players to rely on a slower public stream.

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