The suit was filed against CACI Inc. and Titan Corp. in a US federal court in California on Wednesday on behalf of several prisoners and the estate of one who died at the notorious Iraqi prison.
The lawsuit aims for class-action status, which would allow other prisoners to join, according to the Center for Constitutional Rights, the non-profit group that filed the action.
Instead of providing lawfully contracted services to the US government, the firms "conspired with each other and with certain United States government officials to direct and conduct a scheme to torture, rape and, in some instances, summarily execute" the prisoners, the lawsuit alleged.
The suit also names three employees of the contractors, Adel Nahkla, Stephan Stefanowicz and John Israel.
The suit was filed under the Racketeer Influenced and Corrupt Organizations Act (RICO) and the Alien Tort Claims Act.
It alleges the companies "engaged in a wide range of heinous and illegal acts in order to demonstrate their abilities to obtain intelligence from detainees, and thereby obtain more contracts from the government," the Center for Constitutional Rights said. It seeks unspecified damages.
The suit alleges some prisoners were beaten repeatedly, stripped naked, hooded and raped, forced to watch a father being tortured to death, and otherwise abused and humiliated.
"CACI has never entered into a conspiracy with the government, or anyone else, to perpetrate abuses of any kind"
CACI, a technology service firm, vehemently rejected the allegations, calling them "malicious recitation of false statements and intentional distortions."
"CACI has never entered into a conspiracy with the government, or anyone else, to perpetrate abuses of any kind," the company said in a statement.
"The suit alleges a plethora of heinous acts that the company rejects and denies in their totality," it added.
Plaintiffs were identified as Sami Abbas al-Rawi, Mwafaq Sami Abbas al-Rawi and three individuals referred to only as Ahmad, Ismail and Neisef. They also included two unnamed people and the estate of one person who died, identified only as Ibrahim.