Officials from Google, Facebook, AT&T and Apple will be on the Capitol Hill hot seat Tuesday at a Senate Commerce Committee hearing on online privacy.

The session comes at a time when lawmakers have expressed increased concerns that the new and rapidly growing social communication companies have not done enough to ensure that the information they collect is protected.

A Senate aide said that while companies use information to better tailor services to online users, “there is a concern, however, that tracking individuals’ online activity, gathering information from online users, or selling such information violates consumers’ expectations of privacy.”

The aide said that at the hearing the committee will “further explore the obligations of online companies to adequately notify consumers and obtain their consent for such practices and the role of the federal government in requiring threshold notice, consent and security protocols.”

Company officials scheduled to testify include Bud Tribble, vice president of software technology for Apple Inc.; Bret Taylor, chief technology officer at Facebook; Dorothy Atwood, senior vice president and chief privacy officer for AT&T; and Alma Whitten, lead privacy engineer for Google.

The committee also will hear from Federal Communications Commission Chairman Julius Genachowski and Federal Trade Commission Chairman Jon Leibowitz.

In recent years, the Internet companies have increased their lobbying presence in Washington, D.C., as Congress and the federal agencies have grappled with privacy concerns and other issues.

Facebook, which hired its first D.C. employee in 2007, spent $101,000 on lobbying in the first six months of this year, including $60,000 in the second quarter.

Google shelled out $2.7 million in the first six months of 2010, including $1.3 million in the second quarter. Apple spent $890,000 in the first half of the year, including $330,000 in the second quarter. AT&T, which like other phone companies has long had a large Washington operation, spent $9 million in the first half of this year, including $3 million in the second quarter.

Also on Wednesday, the House Judiciary Subcommittee on Crime, Terrorism and Homeland Security will hold a hearing on online privacy, social networking and crime victimization.