Surrounded by the skyscrapers that tower over Times Square, a new billboard went up this week that in large black letters reads: “NO GAYS ALLOWED.” Just below, a smaller message states: “STOP Alliance Defending Freedom. Learn more at NoGays.org.”

The billboard is part of a new campaign that aims to draw attention to the conservative Christian legal group Alliance Defending Freedom, or ADF, which has been labeled an anti-LGBTQ “hate group” by the Southern Poverty Law Center, a designation the group disputes. Since its founding nearly 25 years ago, ADF has been linked to efforts seeking to criminalize homosexuality, restrict transgender people’s access to sex-segregated facilities and permit businesses to deny service to LGBTQ people.

Caleb Cade, a spokesman for Citizens for Transparency, the advocacy group behind the campaign, said the powerful nonprofit law group has fought for years to undermine lesbian, gay, bisexual, transgender and queer rights, often behind the scenes.

“We want to remind people that there are still really insidious forces at work against our community,” Cade told NBC News. “ADF has been leading that war for a long time, with tens of millions of dollars to do it.”

The Times Square billboard, which went up Tuesday and is expected to remain through February, directs viewers to the campaign’s website, which provides information about ADF’s past works and links to news articles about its efforts to “make LGBT people second-class citizens.”

In response to the newly launched campaign, ADF’s senior counsel, Jeremy Tedesco, shot back at Citizens for Transparency, calling it “an anonymous group that simply copies and pastes false claims" of the Southern Poverty Law Center.

“ADF is one the nation’s most respected and successful Supreme Court advocates, working to preserve our fundamental freedoms of speech, religion and conscience,” Tedesco wrote in an email to NBC News. “ADF is not litigating any cases, pursuing any legislation, nor supporting the passage of any laws domestically or internationally that criminalize sodomy.”

“RELENTLESSLY EXTREME”

ADF was founded in 1994 by a group of influential Christian leaders, including Alan Sears, co-author of the 2003 book "The Homosexual Agenda: Exposing the Principal Threat to Religious Freedom Today,” and James Dobson, founder of Focus on the Family and author of the 2004 book “Marriage Under Fire,” which claimed same-sex marriage would “destroy the fundamental principles of marriage, parenthood and gender.”

Heidi Beirich, director of the Southern Poverty Law Center’s Intelligence Project, said her organization first became aware of ADF in 2013, when it discovered the nonprofit was advising anti-LGBTQ organizations overseas — in places including Belize and Jamaica — on how to keep anti-sodomy laws on their books.

"If there’s an outrageous and ill-founded lawsuit happening against trans people, it’s usually the ADF."

Their efforts to criminalize same-sex sexual activity, however, go back much further than 2013. In the landmark Supreme Court case Lawrence v. Texas, which struck down the remaining anti-sodomy laws in the U.S., ADF (then known as the Alliance Defense Fund) submitted a friend of the court brief in support of keeping the laws on the books.

“There is no fundamental right ‘deeply rooted in this Nation’s history and traditions’ to engage in same-sex sodomy,” the brief concluded.

ADF also contributed to friend of the court briefs against expanding gay rights in other landmark Supreme Court cases, including same-sex marriage cases Obergefell v. Hodges and United States v. Windsor.

“The majority of their work lately,” according to Beirich, “has revolved around religious freedom cases to basically allow certain businesses not to have to serve the LGBTQ population.”

In one of its most recent and high-profile cases, ADF successfully argued a Supreme Court case on behalf of Masterpiece Cakeshop owner Jack Phillips, the Colorado baker who refused to bake a cake for a same-sex wedding because he said it would violate his religious beliefs.

In a case filed last week, ADF is representing a professor who is suing officials at his small public university in Ohio after receiving a warning for violating its nondiscrimination policy by not addressing a transgender student by her preferred gender terms.

In what could be another high-profile case, ADF is urging the Supreme Court to consider a case out of Michigan in which a funeral home fired a transgender employee due to the owner’s religious beliefs. The 6th U.S. Circuit of Appeals sided with the worker, ruling that Title VII of the Civil Rights Act of 1964 protects transgender workers. The funeral home appealed.

Mara Keisling, executive director of the National Center for Transgender Equality, called ADF “the most relentlessly extreme anti-trans law group.”

“If there’s an outrageous and ill-founded lawsuit happening against trans people, it’s usually the ADF,” Keisling told NBC News.

In addition to its work in the courts, ADF has also been linked to so-called transgender bathroom bills that have been introduced in recent years in state legislatures across the U.S. aimed at restricting trans people’s access to sex-segregated facilities.

According to an in-depth NBC News report published in April 2017, many of these “bathroom bills” filed across multiple states resemble one another — and that’s because they used language strongly similar to the model legislation called the Student Physical Privacy Act, which was drafted by ADF.

ADF operates on a budget of over $50 million, according to the Human Rights Campaign, a national LGBTQ rights group. Like any 501c3 nonprofit, ADF is not required to disclose its donors, and many of its 3,200 allied attorneys do not publicize the pro bono work they do on behalf of the organization, which makes the group’s efforts difficult to track, according to Beirich.

FRIENDS IN HIGH PLACES

Despite what many would consider its “extreme” views, ADF has not been relegated to the margins. In fact, Jeff Sessions, then the attorney general, spoke at an ADF event this summer.

During the speech, he thanked the group “on behalf of the president” for its “work and commitment to religious freedom.” He also defended the organization against the Souther Poverty Law Center’s “hate group” label.

“You and I may not agree on everything — but I wanted to come back here tonight partly because I wanted to say this: You are not a hate group.”

Beirich said many people don’t realize the influence the ADF wields. “People just don’t know. They don’t understand that this is the legal arm of the social conservative movement,” she explained.

CITIZENS FOR TRANSPARENCY

While the No Gays Allowed campaign is dedicated to shining a spotlight on ADF, details about Citizens for Transparency itself is not very transparent. The group does not have a website, and when asked about the people behind it, Cade, its spokesman, simply described them as “a group of concerned queer folks that want to fight back against ADF and what they’re doing.”

Cade said the organization is a “501c3 operating under a fiscal agent” and added that the billboard was paid for with $90,000 raised from individual donations.

A statement released about the campaign lists a number of prominent LGBTQ activists that Cade described as “allies” of No Gays Allowed. They include Evan Wolfson, founder of Freedom to Marry; Kate Kendell, executive director of the National Center for Lesbian Rights; Eliza Byard, executive director of GLSEN (formerly the Gay, Lesbian and Straight Education Network); and Christine Quinn, the former speaker of the New York City Council.

Quinn, an out lesbian, told NBC News she hopes the billboard and broader campaign will spur awareness around ADF’s efforts to curtail LGBTQ rights and the challenges the community still faces.

“It’s going to lead people to ask questions,” Quinn said of the campaign. “And that’s really important, to start a conversation, and to have that conversation be in response to this billboard, not the messaging of the ADF.”

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