Lawyers for Russian nationals accused of pushing online propaganda during the 2016 presidential election say Special Counsel Robert Mueller has not shown their clients knew what they were doing was illegal.

The attorneys lay out this somewhat unusual argument in a legal filing posted Monday afternoon. In it, they ask for the judge overseeing the case to review the instructions Mueller’s team gave to the grand jury before it indicted their client, Concord Management and Consulting LLC–which allegedly funded the Kremlin-backed Internet Research Agency. Mueller’s team failed to show “that the Defendant acted willfully, in this case meaning that Defendant was aware of the FEC and FARA requirements,” attorneys Eric Dubelier and Katherine Seikaly of Reed Smith wrote.

Additionally, they write, Mueller accused their clients of a “make-believe crime” in order to advance a “political” agenda of prosecuting people for Russian interference in the U.S. election.

“The risk here is acute,” the filing continues, “that is, a foreign corporation with no presence in the United States is indicted in an unprecedented case of a type never before brought by the DOJ for conspiring to defraud the United States purportedly by not complying with certain regulatory requirements that are unknown even to most Americans.”

At issue is the question of mens rea—the mental state of the Russians who put together the social media disinformation campaign that used Facebook and Twitter to spread fake news stories and socially divisive videos and memes. Attorneys for the Russians are saying that Mueller hasn’t shown their clients knew what they were doing could have been against U.S. law.

Mueller’s indictment alleges that the Russians behind the IRA troll farm used fake American identities to masquerade as supporters of now-President Donald Trump and Sen. Bernie Sanders. (Many of the schemes were first revealed by The Daily Beast.)

The indictment says the IRA started focusing on the United States in 2014. IRA trolls used Facebook, Twitter, Reddit, and other platforms to spread divisive messages and rip into Hillary Clinton. Its monthly budget, per Mueller, was $1.25 million.