The US government has made an agreement with some laser printer manufacturers to encode each page with identifying information, according to civil rights organisation the Electronic Frontier Foundation. 

The activity is being tracked by the American Civil Liberties Union (ACLU) which recently issued a report revealing that the FBI has amassed more than 1,100 pages of documents on the ACLU since 2001, as well as documents concerning other non-violent groups, including Greenpeace and United for Peace and Justice. 

In a statement the EFF said: "We are unaware of any printer manufacturer that has a privacy policy that would protect you, and no law regulates what people can do with the information once it's turned over.

"And that does not even reach the issue of how such a privacy-invasive tool could be developed and implemented in printers without the public becoming aware of it in the first place."

The EFF is gathering information about the data that printers are revealing with a view to a possible legal challenge or to push for new legislation to protect privacy.

Peter Maude, a director of independent testing firm Charisco Printer Labs, said: "I have not heard of this, but I know that the vendors are very concerned about counterfeiting and doing all they can to help catch such fraudsters. 

"It is an activity that damages their reputation so they are naturally keen on any technology that helps to reduce it."

The action follows an article published by PC World in the US in N ovember last year which stated: "Several printer companies quietly encode the serial number and the manufacturing code of their colour laser printers and colour copiers on every document those machines produce.

"Governments, including the United States', already use the hidden markings to track counterfeiters."

There is no suggestion that user information is encoded.

According to the article, the high fidelity of outputs from colour machines suggests that criminals could create high-quality counterfeited currency and government documents using the machines.

At the request of the US Secret Service, manufacturers developed mechanisms that print the serial number and the manufacturer's name in an encoded form as indiscernible markings on colour documents.

The article also claimed that Dutch railway law enforcement officials were employing this same technology to investigate a large-scale ticket counterfeiting operation.

PC World quoted Xerox senior research fellow Peter Crean as saying that each document identification request that Xerox's security department receives from the Secret Service was handled on a case-by-case basis.

It added that Xerox identifies only suspected currency documents, and that the identification of machines used to print pamphlets, letters and other non-currency documents does not occur.