The U.S. Department of Justice on Thursday said it has joined three whistle-blower lawsuits that claim Accenture, Hewlett-Packard, and Sun Microsystems made kickbacks to other companies involved in technology contracts with government agencies.

In its own complaints against the three companies, the DOJ said the defendants solicited and/or made payments of money and other things of value to a number of companies with whom the defendants had global "alliance relationships" or an agreement to work together.

"The government's complaints assert that these alliance relationships and the resulting alliance benefits amount to kickbacks and undisclosed conflict of interest relationships," the DOJ said in a statement.

Accenture and HP issued statements denying any wrongdoing. Both said they were confident they acted appropriately and would "vigorously" defend themselves against the complaints.

Sun said in a statement that the case related to company contracts with the General Services Administration and sales by Sun resellers to various government agencies. The company said a lengthy government audit had been performed on its GSA contracts, but it had not seen the results.

"Sun has fully cooperated with the audit process, as it routinely does, and welcomes the opportunity to review the audit results as soon as permitted and to address the resulting claims in a fair and impartial forum," the company said.

The original whistle-blower suits were filed in U.S. District Court in Little Rock, Ark., by Norman Rille and his co-plaintiff, Neal Roberts. They claimed Accenture, HP, and Sun submitted false claims for IT hardware and services on numerous government contracts from the late 1990s to the present. The core allegations in the suits were the same adopted in the DOJ complaints.

"The Department of Justice is acting in this case to protect the integrity of the procurement process," said Peter Keisler, assistant attorney general for the Civil Division.

The suits were filed under the whistle-blower provision of the federal False Claims Act, which says a person can file an action on behalf of the government and receive a portion of the money recovered. Under the act, the government may recover the amount of its losses, plus civil penalties.

The DOJ filed the complaints April 12 in the Arkansas federal court, which unsealed them Thursday.