Wall Street is reportedly under investigation again for allegedly anti-competitive practices that regulators believe might put small investors at a disadvantage.

About 12 brokerages are the subject of a

Securities and Exchange Commission

probe into whether brokerages ensured that orders for

Nasdaq

stocks were executed at the best possible price, primarily in the early minutes of trading,

The New York Times

reported Monday. The practices being probed are known as internalization and payment-for-order-flow.

Among the investment houses in the SEC's crosshairs reportedly are

Morgan Stanley

(MWD)

,

Merrill Lynch

(MER)

,

Ameritrade

(AMTD) - Get Report

,

Charles Schwab

(SCH)

and

E*Trade

(ET) - Get Report

, the

Times

reported.

The probe is the latest in a series of regulatory efforts to root out conflicts of interest that are sometimes inherent to Wall Street's centuries-old business practices. It follows campaigns by New York Attorney General Eliot Spitzer to end conflicted stock research and mutual fund pricing practices that helped savvy investors make sure-thing bets.

The latest probe comes amid a separate investigation into the way specialist middlemen operate on the

New York Stock Exchange

.

According to the

Times,

the SEC's investigation is looking specifically at internalization, in which a stock broker looks primarily at its own order book to match a buy or sell order, and payment-for-order-flow, in which market makers offer a commission to brokers to handle a stock trade.