Securities and Exchange Commission Chairman William Donaldson cast the deciding vote Wednesday to extend a widely opposed rule that guarantees all investors get the best price on electronic stock trades.

The plan was opposed by companies, including discount broker Charles Schwab and Fidelity Investments, that were concerned the measure would make it more difficult to buy large blocks of stock at a desired price. Rep. Richard Baker, R-La., a prominent member of the House Financial Services Committee also contested the proposal.

"The trade-through rule is, in the most fundamental sense, a rule that protects investors,'" Donaldson said. "Our actions today will, I am certain, irritate a handful of influential interests who are able to couch their arguments in broad principles with which we can all agree."

Donaldson, a Republican, had championed the proposal and got it adopted with the aid of Commissioners Roel Campos and Harvey Goldschmid, both Democrats.

Republicans Cynthia Glassman and Paul Atkins voted against it.

The SEC also voted Wednesday to let Wall Street brokers continue selling investment advice without registering with the commission as advisers.

The 5-0 vote came despite opposition from independent advisers, who argued to the SEC that Wall Street brokers are really just salespeople. The advisers asked the SEC to examine brokers more closely and determine how they market their services to the public

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