The American Civil Liberties Union isn’t exactly known for its sense of humor. But on Aug. 1, the defenders of free speech filed a jocular amicus brief in perhaps the most comical case of 2017, a year that’s proving pretty amusing for US courts.

Still, the organization warns it’s serious about what’s at stake in The Marshall County Coal Company v. John Oliver. In June, a group of coal companies filed a defamation claim in a West Virginia court after unflattering coverage of the industry on an episode of HBO’s weekly show Last Week Tonight With John Oliver.

The June 18 episode covered coal and the industry’s promises to workers. The comedian called coal “basically cocaine for Thomas the Tank Engine” and began by laughing at US president Donald Trump’s pledges that his policies would lead to otherwise under- or unemployed coal miners working their “asses off” during his administration. Oliver soon moved on to mocking industry insiders, like Bob Murray, the CEO of Murray Energy Corporation. The comedian said he’d have to tread carefully with Murray, as the mining baron’s company had already sent him a cease and desist letter.

When Oliver insisted on “being mean” to Murray anyway—in the ACLU’s words—the coal companies filed suit (Murray was named as a plaintiff on the suit). Aimed at Oliver, his senior news producer Charles Wilson, Partially Important Productions, HBO, Time Warner, and “John Does 1-10,” the coal companies’ suit seeks a restraining order and targets a prized American right: speaking freely and having a laugh at someone else’s expense.

In response, the ACLU’s amicus brief accuses Murray of misunderstanding the purpose of the court system in America. According to the ACLU, disliking someone’s satire isn’t a legal matter, and this claim should be dismissed like so many others Murray has filed before. (Murray has a history of suing media companies.)

ACLU The ACLU states its case.

“Although this brief pokes fun at the absurdity of this case, the legal issues raised by it are anything but comical,” the ACLU writes for the defendants. The organization defended the people’s right to be irreverent and the right of the press to be rude.

Indeed, Oliver’s job as the host of a satirical news show is precisely to say and do absurd, provocative, and unusual things. And that’s an American right: the US Constitution protects precisely this kind of speech. The ACLU expressed dismay that any attorney bothered to file such a spurious claim, given American attachment to this particular protection.

The ACLU also asked the court to sanction the plaintiffs for their frivolous legal action. The organization argues that Murray’s history of filing claims whenever he doesn’t like what people says is proof that this suit, too, is just an attempt to retaliate for unflattering media coverage.