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Stocks tanked Monday, the first trading day of the new quarter, as panicked traders dumped their investments in the tech sector amid heightened concern over privacy breaches and continued consumer backlash.

Amazon led the decline, following a series of tweets by President Donald Trump that criticized the company for its effect on retail and its Postal Service "scam."

While we are on the subject, it is reported that the U.S. Post Office will lose $1.50 on average for each package it delivers for Amazon. That amounts to Billions of Dollars. The Failing N.Y. Times reports that “the size of the company’s lobbying staff has ballooned,” and that... — Donald J. Trump (@realDonaldTrump) March 31, 2018

...does not include the Fake Washington Post, which is used as a “lobbyist” and should so REGISTER. If the P.O. “increased its parcel rates, Amazon’s shipping costs would rise by $2.6 Billion.” This Post Office scam must stop. Amazon must pay real costs (and taxes) now! — Donald J. Trump (@realDonaldTrump) March 31, 2018

Shares in the e-commerce giant fell 4 percent Monday after Trump tweeted: "Only fools, or worse, are saying that our money losing Post Office makes money with Amazon. THEY LOSE A FORTUNE, and this will be changed."

The Dow Jones Industrial Average had plummeted by more than 700 points by midafternoon, with the Nasdaq and S&P each down by more than 3 percent.

Bloomberg reported that stocks were on track for their worst April since 1929.

Facebook, Netflix and Alphabet all slumped on Monday as tech titans waged a public war of words. Facebook alone has seen $83 billion scraped off its net worth since the Cambridge Analytica exposé, which revealed that the social media site had enabled data harvesting by a third party.

Wall Street was also reacting to an announcement by China that it planned to impose retaliatory tariffs on 128 American products, including pork, sparkling wine, fruit and nuts, and to comments by Trump indicating that he may tie NAFTA negotiations into his plan for a border wall with Mexico.