IN AMERICA, the fight for free speech sometimes produces odd alliances. Nearly four decades ago, the American Civil Liberties Union (ACLU), a left-leaning advocacy group, famously defended the right of neo-Nazis to march through a neighbourhood in Skokie, Illinois, in which many Holocaust survivors lived. Now a similarly controversial case may be at hand. Yesterday the ACLU filed a complaint in a federal court against the Washington Metropolitan Area Transit Authority (WMATA) for its restrictive advertising policy. Though the suit seeks to vindicate the rights of two organisations on the left of the political spectrum—an animal-rights group and an abortion provider—it is also standing up for a right-wing provocateur’s right to advertise his new book in the subway tunnels of the capital.

Milo Yiannopoulos is no typical conservative. He is a flamboyantly gay former editor at “Breitbart News” who condemns same-sex marriage, tells gays to hide their “aberrant” identity and has targeted black, transgender and Muslim people for ridicule. Last year Twitter banned Mr Yiannopoulos for life after he sent a series of racist messages to Leslie Jones, an actress. In February, the publisher Simon & Schuster pulled out of a contract to publish his book when a video surfaced in which he seemed to say that he was fond of paedophilia.

Adverts in the DC metro for Mr Yiannopoulos’s book “Dangerous”, which he has since self-published, are at the heart of the ACLU’s lawsuit. The suit targets four advertising guidelines which the WMATA imposed in 2015. The ACLU considers the rules unconstitutionally vague and says they discriminate against unpopular views or controversial public figures. One limits “medical and health-related messages” to those matching stances taken by the government or the medical establishment. Another bars messages that bring no “direct commercial benefit to the advertiser”. A third restricts adverts “intended to influence public policy”. Perhaps the worst offender is a rule barring ads “intended to influence members of the public regarding an issue on which there are varying opinions”. This seems to prohibit quite a lot—including pitches for, say, movies (mixed reviews), toothpaste (controversial chemicals) and coriander (some people claim it tastes like soap).

On the basis of these guidelines, the agency rejected several adverts from People for the Ethical Treatment of Animals (PETA), including this one: “Not your mom? Not your milk! DeCalf Your Coffee! Choose almond or soy milk”. A family planning clinic’s message advertising the “10-Week-After-Pill”, an abortion method, was rebuffed too. The ACLU also complained on its own behalf, noting that the WMATA turned down, without explanation, adverts featuring the text of the First Amendment written in English, Spanish or Arabic with the ACLU logo and “We the People” floating above.

In all but one of these examples the WMATA put a halt to the advert before it could grace the subway walls. But the story is different for Mr Yiannopoulos. The agency accepted nearly $28,000 from his company, Milo Worldwide, and the adverts—posters featuring his face, the book title and a brief review quotation—began what was to be a 28-day stint on the metro walls on June 26th. When some riders began to complain, the WMATA said it could not reject advertising simply because “some find it inappropriate or offensive”.

That should have been the end of the story. But on July 6th, less than halfway through the run, the WMATA removed Mr Yiannopoulos’s posters. It offered to return his payment, but Mr Yiannopoulos refused: “You do NOT have our written permission”, his company said, to refund the money. “We consider this to be a violation of our first-amendment rights. If WMATA is intent on pursuing this unconstitutional course of action they should expect to face the full consequences of that”.

It should soon become clear whether the court agrees that the plaintiffs have a constitutional right to place their ads in the capital’s subway cars. They have a good chance: as the ACLU notes, “WMATA’s policy is an attempt to silence anyone who tries to make you think”. According to well-established Supreme Court doctrine, this constitutes a clear violation of the First Amendment—regardless of whether the right to free speech is used to spread hateful messages like those of Mr Yiannopoulos. “If he comes down”, the ACLU says, “so do we all”.