Cable TV, phone and Internet service provider Charter Communications drew concern Friday from two congressmen and a privacy advocate over its plan to experiment with tracking its customers' Web use in collaboration with an online advertising firm.

Charter has told its high-speed Internet customers in four markets about the pilot, which will produce enough information for Web advertisers to target online advertising for individual customers based on their habits.

The ads "will better reflect the interests you express through your Web-surfing activity," Charter senior vice president Joe Stackhouse told the affected subscribers in a letter. "You will not see more ads _ just ads that are more relevant to you."

In response to the announcement, Rep. Edward Markey (D-Mass.) and Rep. Joe Barton (R-Texas) asked Charter President and Chief Executive Neil Smit to put the plan on hold until the three can confer.

The tracking is set to begin in June in Ft. Worth, Texas; San Luis Obispo, Calif.; Oxford, Mass.; and Newtown, Conn.

Jeff Chester of the consumer rights organization Center for Digital Democracy criticized the plan and said it would be the first of its kind among major Internet service providers.

"Charter has moved into the front lines in the battle over ensuring privacy online," Chester said. "There is a huge concern about Web sites and search engine companies tracking what people do."

Stackhouse told customers their personal information will remain confidential.

Subscribers can opt out of the tracking, though they must provide their name and address to install an opt-out cookie on their computer.

Chester said Charter should instead offer subscribers the ability to opt in if they want to participate.

Online ad firm NebuAd is partnering with St. Louis-based Charter to do the tracking. Charter, the nation's fourth-largest cable TV company, is controlled by Microsoft co-founder Paul Allen.

NebuAd, based in Redwood City, Calif., wouldn't say last year how many carriers or advertisers it works with, though CEO Bob Dykes said Internet providers representing millions of customers run NebuAd's system to gather information and get a share of the revenue from advertising that NebuAd places.

NebuAd said then that some of the largest ISPs were testing the service.

NebuAd confirmed Friday that it is partnering with Charter but declined further comment.

Markey, chairman of the House Subcommittee on Telecommunications and the Internet, is concerned about Charter's subscribers' privacy.

Collecting data about the Web habits of subscribers without their prior consent is "raises substantial questions related to Section 631" of the Communications Act, he wrote in a letter to Smit.

The section of the law Markey cited includes privacy provisions for cable operators.

Charter has always taken an "open approach" with its customers, the company said in a statement Friday.

"Our goal is to bring an enhanced Internet experience to our customer while meeting all privacy protection requirements," the company said. "We believe we have done that but are pleased to discuss this matter with the Chairman and the Congressman."

On its Web site, Charter says it will not track _ or display ads related to _ confidential medical information; racial or ethnic origin; religious beliefs or sexual content. And it will not direct ads at children under 13, according to a FAQs page on Charter's Web site.

"This is a kind of 24-7 inside look at everything you do in order to target you with advertising," said

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On the Net:

Charter: http://www.charter.com

NebuAd: http://www.nebuad.com

Center for Digital Democracy: http://www.democraticmedia.org