For torturing them while they were detained at the Abu Ghraib prison, near Baghdad, four Iraqi men say they are suing the US military contractors.
All were released without charge, and have brought separate lawsuits in four US courts.
One of the men said that during four years at the prison, he was beaten, threatened with dogs and given electric shocks.
The claims have been dismissed as “baseless” by CACI International, one of two companies named in the lawsuits.
Three civilians have also been named in the case. They are all said to be former employees of CACI and L-3 Communications Corp, the two contractors.
Adel Nakhla of Maryland, Timothy Dugan of Ohio and Daniel Johnson of Seattle are accused of taking part in abuses during interrogations.
“Unfounded and unsubstantiated” is what CACI said the claims were, and the new lawsuits repeated “baseless allegations” from a previous lawsuit several years ago.
“These generic allegations of abuse, coupled with imaginary claims of conspiracy, remain unconnected to any CACI personnel”, the company said in a statement.
Mr Johnson’s lawyer also said the claims were false, and told the Associated Press that while he was working in Irak, his client had served his country “honourably”.
The four plaintiffs were held in Abu Ghraib prison in 2003 and 2004.
In 2003, when photographs showing US soldier mistreating prisoners emerged, abuses at the prison were brought to light.
Waseem al-Quraishi, one of the plaintiffs, said he was electrocuted, beaten and hung from a pole for seven days.
Another, Mohammed Abdwaihed Towfek al-Taee, says he was forced to drink litres of water while his penis was tied to prevent him from urinating.
Though military personnel have already been tried on criminal charges and imprisoned for abuses at Abu Ghraib, no civilians have.
Tens of thousands of US civilians have worked on contract for the US military in Iraq, many of them in very sensitive roles such as in intelligence gathering and in combat.
One of the most vexed questions of the war is whose laws they should obey, and who should hold them accountable when they do things wrong, said the BBC’s Adam Brookes in Washington.