The U.S. Securities and Exchange Commission may strip Vanguard Group, BlackRock Inc and State Street Corp, the oldest and biggest providers of exchange-traded funds, of an advantage they hold over newer rivals in how they assemble the shares of their funds, said sources familiar with the SEC. ETFs are typically funds whose holdings are meant to mimic the performance of an index. To do that, the SEC has said the securities used to create shares in most funds must be the same ones as in the fund’s portfolio unless there was a change in the index the fund tracks.