The opposition research firm behind the infamous Trump dossier is being sued for defamation in federal court.

The lawsuit, filed on Tuesday by three executives with Alfa Bank, a private commercial Russian bank, is the first filed against Fusion GPS and its founder, Glenn Simpson, since the dossier was published by BuzzFeed on Jan. 10.

Other lawsuits have been filed, both against BuzzFeed and against Christopher Steele, the former British spy who wrote the largely uncorroborated dossier. Alfa Bank’s trio of executives recently filed suit against BuzzFeed, and a Russian tech executive named in the dossier has sued both the news outlet and Steele, who operates a London-based intelligence firm called Orbis.

Steele was hired last June by the D.C.-based Fusion to investigate Donald Trump’s personal and business activities in Russia. He would go on to produce 17 memos of material about the former real estate executive as well as about Russia’s activities during the campaign. (RELATED: Here’s Everything We Know So Far About The Trump Dossier)

One of the memos, dated Sept. 14, 2016, alleges that Alfa Bank executives Mikhail Fridman, Peter Aven and German Khan took part in the Kremlin’s election meddling.

The three executives claim that the allegations are false and that Fusion GPS recklessly distributed the dossier to media outlets for political purposes. Fusion was working at the time for a political ally of Hillary Clinton’s.

In the filing, lawyers for the executives argue that opposition research like the kind commissioned and distributed by Fusion GPS “is neither objective nor neutral.”

“Instead, it is skewed from the outset in favor of appearing to find negative information about individuals — the essence of the product that political opposition research practitioners are hired to produce,” reads the complaint, filed by Alan Lewis and John Walsh of Carter, Ledyard & Milburn law firm.

“Even though the Dossier contained unverified allegations, Defendants recklessly placed it beyond their control and allowed it to fall into the hands of media devoted to breaking news on the hottest subject of the day: the Trump candidacy.”

The executives also assert that Fusion GPS “could have easily removed” the memo identifying the company from the dossier before “they started peddling” the document to media outlets.

“They chose not to do so. Nor did they attempt to determine the veracity of that Report with the Plaintiffs themselves,” their complaint reads.

It also notes that Steele has said in court filings in London, where he is being sued, that he was unable to verify some parts of the dossier. The former MI6 agent, who previously worked in Moscow, was not directly provided the information that ended up in the document. Instead, he paid sources and sub-sources for the information.

The lawsuit could shed light on some of the mysteries surrounding Fusion’s work during the campaign, as well as about the ongoing investigation into possible collusion between the Trump team and Russian government.

Fusion and Simpson, a former Wall Street Journal reporter, have refused to identify its pro-Clinton client. Simpson, who was interviewed by the Senate Judiciary Committee in August, has also refused to name a wealthy anti-Trump Republican who hired Fusion in September 2015 to investigate Trump. That client dropped from the project after Trump secured the GOP nomination. Steele was hired soon after. (RELATED: Fusion GPS Founder Refuses To Identify Dossier Clients During Marathon Senate Session)

The FBI has also reportedly used the dossier as part of the basis for its collusion investigation. The bureau reportedly cited the dossier in its application for a Foreign Intelligence Surveillance Act warrant against Carter Page, a former Trump campaign adviser who is accused in the dossier of serving as the middleman between the Trump campaign and Kremlin.

Page, a New York-based energy consultant, has denied the allegations in the Steele document, which he calls the “dodgy dossier.”

Some Republican lawmakers have pressed the FBI about how much it relied on the dossier for its investigation into the Trump campaign, which began last July. They have also asked about reports that the FBI struck an informal agreement with Steele last October to pay him $50,000 to continue his Trump investigation.

In response to the lawsuit against him in London, Steele has acknowledged that he and Fusion GPS briefed reporters last year at outlets like Yahoo! News, Mother Jones, The New York Times and The Washington Post about some of the claims in the dossier. Steele said in court filings that Fusion GPS directed him to provide the briefings, which were conducted off-the-record. (RELATED: Details Emerge About Fusion GPS’ Media Outreach Campaign)

It is still not entirely clear whether Fusion distributed the dossier to BuzzFeed, though that is the most popular theory. The Alfa Bank executives noted in their complaint that Fusion GPS recently stated in a separate lawsuit against BuzzFeed that it would disclose communications it had with the website and its editor, Ben Smith.

Notably, one of the attorneys representing the executives as local counsel is Kim Sperduto, the founder of the law firm Sperduto Thompson. Lewis and Walsh of Carter, Ledyard & Milburn will serve as lead counsel.

Sperduto has in the past represented Rinat Akhmetshin, the Russian-American lobbyist who took part in the now-infamous June 9, 2016, meeting in Trump Tower with members of the Trump campaign.

At the time, Akhmetshin was working on a lobbying campaign against the Magnitsky Act, a sanctions law passed in 2012 that blacklists Russians accused of human rights abuses. Fusion GPS and Simpson were also working on that project alongside Akhmetshin. (RELATED: Fusion GPS Is Linked To Pro-Kremlin Lobbying Effort)

The Daily Caller has been told by sources who know Simpson and Akhmetshin that the two have known each other for more than a decade and have also collaborated in the past, beginning when Simpson worked as a reporter for The Wall Street Journal.

A representative for Fusion did not respond to TheDC’s request for comment about the lawsuit.

This article has been updated to note that the lawsuit was filed by Alfa Bank’s executives and not by the bank itself.

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