Technology stocks tumbled on Monday, as declines in the biggest companies in the sector punctuated an otherwise quiet day on Wall Street.

Google, Amazon, Facebook and Apple were all lower, following reports that the tech giants are facing greater scrutiny from antitrust regulators in the Justice Department and Federal Trade Commission. The technology-heavy Nasdaq index fell by 1.6 percent, bringing its decline from an early May record to 10 percent.

Regulators appear to be splitting up oversight of the four companies. The Justice Department is exploring an investigation of Google’s advertising and search business, and will oversee antitrust complaints over Apple. The F.T.C. will look into anticompetitive practices at Amazon and Facebook.

The delegation of responsibility does not mean that official investigations have been opened, or will be.