In a letter sent to Google CEO Eric Schmidt this week, Rep. Joe Barton (R-Tex.), ranking member of the House energy committee, asked the company to provide details about how it will use data about consumers from DoubleClick.

"It is critical that Google's and DoubleClick's policies and procedures for handling this information be transparent, and that every effort is made to protect consumers' data," he wrote.

Google has a trove of information about the search queries originating from specific IP addresses, while DoubleClick has cookie-based ad-serving data about users. Privacy advocates who opposed the companies' $3.4 billion merger said they were concerned that Google would combine its search data with DoubleClick's data across a variety of sites to compile detailed profiles about individual Web users.

Barton's three-page letter contained a host of pointed privacy-related questions, including whether Google plans to merge cookie data from DoubleClick, whether Google will continue to let users opt-out of DoubleClick's ad-serving cookie, and the length of time for which Google will retain information about the IP addresses of users it serves ads to.

Barton also called on Google to clarify information about DoubleClick's contracts with advertisers. The companies have said that existing agreements prohibit DoubleClick from sharing information about users' Web-surfing activity with Google, even though Google now owns DoubleClick. Barton pressed for further details about those agreements and also asked whether Google intends to renegotiate those deals.

The lawmaker asked Google to respond to the letter by June 6.

Google spokesman Adam Kovacevich said the company is talking with Barton's staff. "We have had a constructive ongoing dialogue with Rep. Barton's staff about our privacy practices, and while the integration of DoubleClick into Google is still underway, we will of course respond to his questions," he said.

This week's letter is not the first time Barton has raised privacy issues with Google. Late last year, the lawmaker also questioned Google about similar issues. He met with Google's Schmidt in private last November and his staff traveled to Google's Mountain View, Calif. headquarters in December for briefings about the company.