Apple will see its portion of the Nasdaq-100 Index reduced to reflect new benchmark changes as the iPhone maker has its weighting cut from over 20% to 12.3%.

Meanwhile, the weightings of Microsoft and Cisco in the Nasdaq-100 will rise, affecting the $24.4 billion PowerShares QQQ (NasdaqGM: QQQ), one of the largest exchange traded funds (ETFs).

Nasdaq OMX Group in a press release said the index will undergo a “special rebalance” prior to the market’s open on May 2. The rebalancing will not change the methodology used to calculate the Nasdaq-100 Index or the benchmark securities, the company said.

The change “reflects our commitment to ensure the Nasdaq-100 Index remains a relevant benchmark for investors around the world who track the performance of the U.S. equity market,” said John Jacobs, executive vice president at Nasdaq OMX Global Index Group. The benchmark will remain “an objective, transparent, rules-based index,” he said in the release.

The surge in Apple shares the past two years contributed to the decision to rebalance the index, The Wall Street Journal reported Tuesday.

A Nasdaq spokesman didn’t immediately return a request for comment Tuesday morning.

The special rebalancing is adjusting index stocks to “bring the weights closer in line with their actual market capitalizations,” according to slides prepared by Nasdaq.

For every $1 billion benchmarked to the Nasdaq-100, an estimated 9.5 million shares will trade, according to the presentation. The rebalancing will be felt in markets as passive managers buy and sell stocks to reflect the new weightings. Apple shares in particular should see selling pressure due to the company’s expected dramatic reduction in the Nasdaq-100.

Apple shares were lower in Tuesday’s premarket while Microsoft traded higher.

“It’s going to be a big trade,” Nasdaq’s Jacobs told the WSJ. However, “we wanted to make this very transparent. Everyone will see what we’re doing and everyone will have a month before we do this,” he told the newspaper.

PowerShares QQQ is up about 5% so far this year.