emails from US-based intelligence firm Stratfor, the anti-secrecy group said.
The messages, which date from between July 2004 and December 2011, allegedly show that Dow Chemicals used Stratfor to monitor and analyse the online activities of activists seeking redress for the 1984 Dow Chemical/Union Carbide gas disaster in Bhopal.
WikiLeaks promises it will reveal Stratfor's "web of informers, pay-off structure, payment-laundering techniques and psychological methods," claimed a WikiLeaks press release.
"The material shows how a private intelligence agency works, and how they target individuals for their corporate and government clients," added the press release.
The online organisation claims to have proof of the firm's confidential links to large corporations, such as Bhopal's Dow Chemical Co and Lockheed Martin and government agencies, including the US Department of Homeland Security, the US Marines and the US Defense Intelligence Agency.
Stratfor described the action as "deplorable and illegal breach of privacy." In a statement the company added, "Some of the emails may be forged or altered to include inaccuracies; some may be authentic. We will not validate either. Nor will we explain the thinking that went into them. Having had our property stolen, we will not be victimized twice by submitting to questioning about them."
WikiLeaks founder Julian Assange is currently in Britain fighting extradition to Sweden where he is wanted for questioning on rape and sexual assault allegations, and WikiLeaks has long expressed concern that if he is sent to Sweden, Stockholm would quickly send him on to the United States.
Washington is eager to lay hands on the founder after the organisation's publication of hundreds of thousands of classified US diplomatic files.
WikiLeaks promises that the latest leak will highlight Stratfor's attempts to "subvert" the website and expose the US's attempts to "attack" Assange.
Stratfor, which was founded by George Friedman in 1996, describes itself as "a subscription-based provider of geopolitical analysis."
"Unlike traditional news outlets, Stratfor uses a unique, intelligence-based approach to gathering information via rigorous open-source monitoring and a global network of human sources," according to the Texas-based firm's website.
The company promises subscribers will "gain a thorough understanding of international affairs, including what's happening, why it's happening, and what will happen next."
WikiLeaks predicts that the significance of the emails will only become clear over the next few weeks as its 25 media partners and the public sift through the raft of messages.
Its media partners include Rolling Stone magazine, The Hindu newspaper and Italy's La Repubblica.
The group claims to have found evidence that Stratfor gave a complimentary membership to Pakistan general Hamid Gul, former head of Pakistan's ISI intelligence service, who, according to US diplomatic cables, planned an IED attack against international forces in Afghanistan in 2006.
Bradley Manning, the man suspected of turning over a massive cache of classified US documents to the secret-spilling site, on Thursday declined to enter a plea at his arraignment.
Manning, a 24-year-old US Army private, is charged with 22 counts in connection with one of the biggest intelligence breaches in US history.
WikiLeaks was due to hold a press conference at London's Frontline Club later today.
(With AFP inputs)