NEW YORK (CNNMoney.com) -- The House Energy and Commerce Committee said Wednesday it subpoenaed five private investigators to testify at a hearing on Hewlett-Packard's leak probe.

The committee said it subpoenaed five pretexters: Bryan Wagner, Littleton, Colo.; Charles Kelly of CAS Agency, Villa Rica, Ga.; Cassandra Selvage of Eye in the Sky Investigations, Dade City, Fla.; Darren Brost, Austin, Texas; and Valerie Preston of InSearchOf Inc., Cooper City, Fla.

Pretexting is a practice where personal confidential information is obtained through false pretenses. It is the subject of a hearing on HP's (Charts) spying scandal set for Thursday.

The House panel has already subpoenaed Ronald DeLia, managing director of Security Outsourcing Solutions, and two HP executives, Kevin Hunsaker and Anthony Gentilucci.

HP has said chief executive Mark Hurd, recently ousted chairman Patricia Dunn and general counsel Ann Baskins will also testify at the hearing.

The HP hearing is part of a wider inquiry into pretexting that has been building in Congress for months.

Shares of HP edged lower in midday trading. Shares of rivals Dell (Charts) and IBM (Charts) also fell.

HP lights the privacy powder keg

Hewlett-Packard heads to the Hill