Shares of Google (Nasdaq: GOOG), the No. 1 search engine, fell after the U.S. Federal Communications Commission said it had tried to impede a privacy investigation.

The FCC also said it will fine the Mounatin View, Calif., giant $25,000. Google reported cash and investments of $49.3 billion as of March 31.

Shares of Google fell 3 percent to $606.07, down $18.53, in Monday trading. Google admitted a mistake in the way in which it collected data from its millions of users but said it's now working with regulators.

The FCC, in a filing, alleged that Google violated privacy rules for its Street View location services by collecting unnecessary content from wireless networks. That content included e-mail, text messages, passwords and other browsing history.

Google has acknowledged it's being probed for possible antitrust violations by the U.S. Department of Justice, the Federal Trade Commission and the European Commission. No charges have been brought but Google has beefed up its legal staff by including some formal federal investigators.

In its filing, the FCC claimed Google initially denied collecting payload data - or sensitive user information - but then acknowledged it had done so but only fragmented data.

After subpoenaing Google engineers for many months Google deliberately impeded and delayed the probe and repeatedly violated Commission orders to produce certain information. A Google engineer invoked the Fifth Amendment rather than comply with an FCC subpoena, the agency said.