WASHINGTON — Concerned about the growing reach of data brokers into the day-to-day lives of Americans, members of Congress, including Representative Edward Markey of Massachusetts, are demanding answers from the some of the country’s biggest collectors of personal data as part of a fact-finding process that could lead to regulating the lucrative industry.

Many consumers are unaware about the extent they are being tracked, when they shop for groceries, buy airline tickets, or click through their favorite Internet sites.

In letters to nine of data brokers, the bipartisan group of eight elected officials noted the rising concerns over how the data is being amassed — from age, race, marital status and education level to political leanings, buying habits, and health conditions of an individual.

“By combining data from numerous offline and online sources, data brokers have developed hidden dossiers on almost every US consumer,” the letters said.

In addition to Markey, the letters were signed by Representative Joe Barton, a Republican from Texas. The two co-chair the Congressional Bipartisan Privacy Caucus.

“The aggregation of personal details for sale to marketers has the potential to affect nearly all Americans, but children and teens are particularly at risk. Because of this, we have questions concerning whether you are collecting information about children and teens and, if so, what kind of information you are collecting,” the lawmakers said.

The letters enumerate 14 areas of inquiry, including a request for the companies to list the types of data collected by the firms since 2009, whether consumers are allowed access to the information being collected by them, and whether protocols are in place to correct incorrect information.

Requests were made to the data brokers Acxiom, Epsilon, Equifax, Experian, Harte-Hanks, Intelius, FICO, Markle, and the Meredith Corp.

Consumers “often have little or no knowledge about the identity of data brokers, how they collect personal information, and to which outside parties they sell or otherwise provide this information,” the letters stated.