Some of the biggest names in online advertising and internet access received a letter from U.S. lawmakers last week, as the government continues to debate online privacy and investigate ad-targeting practices.

Members of the House Energy and Commerce Committee wrote to more than 30 online companies, including Comcast, AT&T, Verizon, Google and Microsoft, asking if they "tailored, or facilitated the tailoring of, internet advertising based on consumers internet search, surfing, or other use," according to an Associated Press report.

Some of the questions in the letter concern where ad targeting has been used, how many consumers have been subjected to it and whether or not those consumers were aware of the process.

The privacy debate seems to be growing louder lately, but advertisers scored a major ally a few weeks ago when Lydia B. Parnes, the director of the FTC's bureau of consumer protection, said she favored industry self-regulation over government standards.