The major equity indexes end the day in negative territory on Monday, with the S&P and Nasdaq suffering their worst day in just over five weeks, as concerns over increased regulation for large tech companies was spearheaded by a plunge in Facebook shares.

Facebook closed down 6.8 percent as Chief Executive Mark Zuckerberg faced calls from both U.S. and European lawmakers to explain how a consultancy that worked on President Donald Trump’s election campaign gained access to data on 50 million Facebook users.

The stock had its worst day since March 2014 and was down 10.8 percent from its closing record hit on Feb. 1, resulting the shares being squarely in correction territory, a drop of 10 percent from its high.

Facebook’s decline weighed heavily on the S&P technology sector, down 2.11 percent, as well as the Nasdaq, off more than 2 percent. Both indexes had their worst daily performance since Feb. 8.

Other major companies with large tech businesses also fell as recent concerns over regulation in the arena increased. Apple lost 1.53 percent while Alphabet fell 3 percent and Microsoft declined 1.8 percent.

The S&P once again fell below its 50-day moving average, seen as a technical support level, for the first time since early March. The Nasdaq came about 2 points from its 50-day before paring losses.

Investors were also cautious ahead of a two-day monetary policy meeting at the U.S. Federal Reserve starting on Tuesday.

The market believes the Fed is set to raise interest rates on Wednesday as Thomson Reuters data shows traders expect a quarter-percentage-point hike to be a certainty.

Investors are now grappling with the question of whether an improving economy could lead to more hikes than anticipated.

Industrials fell 0.82 percent against the backdrop of worries about a global trade war, which are set to dominate a two-day G20 meeting in Argentina.

Selling was broad, with each of the 11 major S&P sectors in the red. The CBOE Volatility index touched a high of 21.87 in one of its sharpest gains since the market sell-off in February.

Approximately 6.9 billion shares changed hands on the major domestic equity exchanges, as compared to the 7.2 billion share average over the past 20 trading days.