He said he was particularly troubled by data broker programs that categorize individual consumers as desirable or undesirable sales prospects, often without their knowledge and consent, a practice that he said raised privacy concerns. “I’m hoping to ratchet up the transparency so we can foster a system of oversight and consumer control over their data.”

The privacy caucus’s letter was prompted by an article last month in The New York Times about Acxiom, based in Little Rock, Ark. Mr. Markey’s office gave The Times a copy of the letter.

Jennifer Barrett Glasgow, the chief privacy officer of Acxiom, said company executives had testified before Congress numerous times to inform legislators about the steps they take to protect consumers. “We are happy to provide whatever information we can to further inform interested parties,” she said.

Other industry representatives did not immediately respond to requests for comment.

The privacy caucus does not have subpoena power. But Mr. Markey said other industries, like cellphone carriers, had complied with his requests in the past. He said he expected similar cooperation from data brokers.

The letter asked each company to provide a list of all of its sources of data; a list of the specific kinds of consumer information, including ethnic, race or religious data, it collects; descriptions of the data collection methods used, like tracking of social network or mobile phone activity; explanations about each product and service the company has marketed to third parties since January 2009, and the type of data used in such products and services; details about whether any of the products or services are federally regulated; explanations about the security measures used to protect consumer data; as well as descriptions of the opt-out, data access, correction and deletion options the company offers consumers.

The direct marketing industry already offers consumers choices about managing marketing pitches sent through the mail. Digital marketers have a program for people who wish to opt out of receiving online ads tailored to their behavior.

But Mr. Markey said consumers also needed greater access to data collected about them so they could make more informed choices.

“You have to make sure that the values of the physical world accompany the transition to the virtual, digital world,” he said.