(Adds details on decision, background)
NEW YORK, June 21 (Reuters) - Stock index provider MSCI said on Thursday it extended its review of how to treat stocks with unequal voting rights and expects to make a decision by the end of October.
That decision, which could affect dozens of stocks around the world, including technology heavyweights Facebook and Google parent Alphabet, had been expected by Thursday.
But MSCI said in a statement that it "determined that it is appropriate to give further consideration to the full breadth of views expressed by the investment community before announcing a final conclusion."
MSCI has been considering a plan to reduce the influence within its indexes of stocks that have share structures with unequal voting rights. Such a move could have resulted in portfolio managers selling their shares to rebalance their holdings.
More than $660 billion in passively managed funds track MSCI indexes around the world, according to Lipper data.
Uneven voting structures has been a hot corporate governance topic, especially as a number of newly listed U.S. technology firms, such as Snap Inc and Dropbox Inc, have listed shares that retain lopsided decision-making power with insiders.
Last year, S&P Dow Jones Indices started excluding companies with multiple classes of shares from the S&P 500 and other indexes, although it did not apply the rule to existing index components, including Alphabet and Berkshire Hathaway Inc .
FTSE Russell implemented a similar rule last July, requiring new constituents of its indexes to have at least 5 percent of their voting rights in the hands of public shareholders, while giving a five-year grace period to existing constituents that do not meet the threshold.
The MSCI proposal, made in January, has not been universally welcomed.
BlackRock Inc, the world's largest asset manager, in April said securities regulators, not index providers, should set international standards for shareholder voting rights. It said MSCI's proposal could distort markets. (Reporting by Lewis Krauskopf and Noel Randewich; editing by Bill Berkrot)