Reacting to a recent series of articles in The Wall Street Journal, Reps. Ed Markey (D-Mass.) and Joe Barton (R-Tex.) sent letters to 15 Internet companies questioning their practice of allowing third-party advertising companies to install cookies and other tracking mechanisms on visitors’ computers.

The WSJ series, called “What They Know,” told readers that “Marketers are spying on Internet users – observing and remembering people’s clicks, and building and selling detailed dossiers of their activities and interests.” The publication looked at the top 50 Web sites in the United States and found that these sites dropped an average of 64 pieces of tracking technology – like cookies – onto users’ computers.

Writing to companies including AOL, Yahoo, and MSN, the legislators said they were “troubled” by the findings in the articles, which they said raised “important questions about the nature, scope and prevalence of Internet companies’ use of consumers’ personal information gleaned from their online activities, reportedly without consumers’ knowledge or consent.”

“This data gathering permits web-based enterprises to develop digital dossiers on consumers for a range of purposes, including highly targeted marketing,” the lawmakers wrote.

Recipients of the letters were asked to respond to questions including what specific information they collect from consumers, whether the information is monetized, and if so, how much revenue is associated with the information over a 12-month period.

The companies were also asked about privacy policies and whether they offer consumers the ability to opt-in to or opt-out of collection practices, or allow consumers the option to prevent the collection and use of their data.

To read one of the identical letters sent to all 15 companies, click here.

Why it matters: The letters requested answers from the companies by August 12, giving legislators time to consider the responses as they begin debating pending privacy legislation. Although Rep. Rick Boucher (D-Va.) circulated a draft of his proposed law first, he recently said that his bill will likely be merged with legislation introduced by Rep. Bobby Rush (D-Ill.), the Best Practices Act.