Brokers could be required to tell investors exactly where theysent a stock order to be filled under a measure the U.S. Securitiesand Exchange Commission (SEC) is weighing to address complaintsthat the decisions sometimes aren't in clients' best interests.

The proposal could give investors more insight into whether theyare getting the best price when they buy and sell large numbers ofshares, according to three people familiar with the matter. Brokersentrusted with orders in the U.S. stock market can choose fromdozens of exchanges and private venues. Some money managers such asT. Rowe Price Group Inc. have told regulators that incentivesoffered by exchanges for attracting orders can put a broker'sfinancial interest at odds with the customer's.

The SEC faces pressure to overhaul trading after Michael Lewis's“Flash Boys” book made the claim that high-frequency traders hurt other investors by learning whichshares investors plan to buy, purchasing them, and selling themback at a higher price. The SEC has said it's reviewing everyaspect of how stocks are traded, and regulators are trying toidentify changes that could be implemented quickly, the peoplesaid.