An ACLU attorney who represented Chelsea Manning is blasting the organization's decision to defend conservative provocateur Milo Yiannopoulous in a lawsuit against Washington D.C.'s public transit agency.

The American Civil Liberties Union on Wednesday announced they were suing the Washington Metro Area Transit Authority over its refusal to display ads promoting Milo Yiannopoulos' book.

"I don't believe in protecting principle for the sake of protecting principle in all cases," Chase Strangio said in a statement.

Strangio argues Yiannopoulos' behavior may not necessarily fall under the legal definition of incitement but his actions do "exacerbate harm" to the black and transgender communities.

"The ACLU has a long history of representing despicable people in the service of protecting valuable First Amendment principles and in some cases I support decisions that have been made and in other cases I do not. Here I do not," Strangio said.

The ACLU's lawsuit argues parts of WMATA's ad policies violate the First Amendment by discriminating against particular ads and advertisers deemed controversial by WMATA officials.

Metro's policies first came into place in 2015 after a set of anti-Muslim advertisements sparked controversy. Current guidelines ban ads "intended to influence members of the public regarding an issue on which there are varying opinions," ads that "support or oppose an industry position or industry goal without any direct commercial benefit to the advertiser," and ads "intended to influence public policy," among others.

"This case highlights the consequences of the government's attempt to suppress all controversial speech on public transit property," Arthur Spitzer, legal director of the ACLU-DC and lead counsel in the case, said in a statement Wednesday. "The First Amendment protects the speech of everyone from discriminatory government censorship, whether you agree with the message or not."

"The ACLU could not more strongly disagree with the values that Milo Yiannopoulos espouses, but we can't allow the government to pick and choose which viewpoints are acceptable," said Lee Rowland, senior staff attorney with the ACLU.

The suit asked the court to declare portions of the WMATA advertising guidelines unconstitutional because they violate free speech rights and are unconstitutionally vague. A motion has also been filed on behalf of Milo Worldwide LLC, seeking immediate financial restitution for the ongoing loss of revenue from book sales caused by what they deem the wrongful removal of advertisements for his book.