Volatility could well be in the cards for Wall Street again early this fall, but not for the same reason stocks got rattled in February.

This time the culprit would be the largest-ever shakeup of the stock market’s broad business sectors, which will mean some of the hottest stocks, like Facebook and Google parent Alphabet, will shift from their traditional homes in the top-performing technology sector and into a deepened pool of telecommunications and media stocks.

The sweeping reorganization of the Global Industry Classification Standard, or GICS, means that funds tracking the telecom, tech and consumer discretionary sectors will be forced to trade billions of dollars of stock to realign their holdings by a Sept. 28 effective date.

While the choppiness many investors expect to see is unlikely to hit stocks in quite the same way that wave of the global uncertainty did in early 2018, the fact that so much money must be shifted among index funds in a short time will cause a stir.

In a bid to ensure a smooth transition, leading fund provider Vanguard Group has have already started adjusting its sector exchange-traded funds, or ETFs, while State Street Global Advisors is launching an entirely new fund.

Other investors predict price swings and commotion on trading desks if last-minute sales of Alphabet and Facebook shares by heavyweight technology index funds dwarf demand from a handful of telecom funds buying those stocks.

“There’s probably going to be net selling,” said Andrew Bodner, president of Double Diamond Investment Group in Parsippany, New Jersey. “That will be a temporary scenario, and it could be a good buying opportunity for a lot of those stocks.”

Maintained by S&P Dow Jones Indices and MSCI since 1999 and widely used by portfolio managers, the GICS classifies companies across 11 sectors. The newest, real estate, was split off from financials in 2016. The upcoming changes, which have yet to be finalized, are meant to reflect evolving industries.

Facebook and Alphabet will move from information technology and sit alongside AT&T Inc and Verizon Communications in a broadened telecommunication services sector that will be renamed communications services.