Reps. Edward Markey, D-Mass., Joe Barton, R-Texas, and Cliff Stearns, R-Fla., said they want to know whether Google's behavior "constitutes a violation" of a privacy settlement Google Inc. and the commission worked out last year.
Google pledged at the time not to "misrepresent" its privacy practices to consumers. The fine for violating the agreement is $16,000 for every violation each day.
Google and three other advertising companies used special computer code that tricks Apple Inc.'s Safari Web-browsing software into letting them monitor users' Internet habits -- even though Safari, the most-widely used smartphone Web browser, is designed to block such tracking by default.
"Google's practices could have a wide-sweeping impact because Safari is a major Web browser used by millions of Americans," Markey and Barton wrote in a letter to the FTC. "As members of the Congressional Bi-Partisan Privacy Caucus, we are interested in any actions the FTC has taken or plans to take to investigate whether Google has violated the terms of its consent agreement."
The FTC had no immediate comment.
A Stanford University graduate student in computer science and law released a report this week accusing Google and the other ad networks of sidestepping the privacy settings on Apple's Safari browser to track usage on iPhones and Macs without permission.
The Wall Street Journal picked up the report Friday.
Google disabled its code after the Journal contacted it, the newspaper said.
The Mountain View, Calif., company said the Journal "mischaracterizes what happened and why."
"We used known Safari functionality to provide features that signed-in Google users had enabled," Google said. "It's important to stress that these advertising cookies do not collect personal information."
The three other online ad companies found using similar techniques are Vibrant Media Inc., WPP PLC's Media Innovation Group LLC and Gannett Co.'s PointRoll Inc.
A Vibrant Media spokesman told the Journal the technique was a "workaround" to "make Safari work like all the other browsers."
WPP declined to comment.
A Gannett spokeswoman described the company's use of the code as a "limited test" to see how many Safari users visited advertisers' sites after seeing an ad.
A Google site earlier told Safari users they could rely on Safari's privacy settings to prevent tracking by Google. Google removed that language from the site Tuesday night, the Journal said.
An Apple official told the Journal, "We are working to put a stop" to the circumvention of Safari privacy settings.