Over 80 prominent American civil rights and faith-based groups have come out against President Donald Trump’s reported plan to designate the Muslim Brotherhood a terror organization, arguing it would provide a smokescreen to smear and persecute American Muslims and shut down important Muslim organizations.

An open letter published Thursday by the American Civil Liberties Union, the Council on American-Islamic Relations, Human Rights Watch, Amnesty International, the Brennan Center for Justice, and dozens of faith-based and social justice groups argued the terror designation could give a White House already hostile to Muslims the power to lead a “witch-hunt against Muslim society in the U.S.”

The designation, the letter states, would allow the administration to “destroy reputations and chill lawful activity,” and “runs the serious risk of stifling religious and political freedom and the ability to assist and represent Muslim communities without fear of retaliation.”

Anti-Muslim groups in the U.S. have long salivated over the prospect of designating the Muslim Brotherhood ― a culturally conservative political movement founded in Egypt to push for Islamic-based governments ― as a foreign terror organization.

For years, these groups have promoted paranoid conspiracy theories wherein the brotherhood is actively coordinating a massive, subversive plot among American Muslims to destroy the U.S. from within.

Thursday’s letter notes how right-wing groups and leaders have for years “used false ‘six degrees of separation’ accusations about the Muslim Brotherhood as a way to smear prominent Muslims, American Muslim civic and religious institutions, as well as a range of other people.”

CAIR and the Islamic Society of North America ― and everyone from Hillary Clinton aide Huma Abedin to conservative activist Grover Norquist ― have been baselessly accused of working for the brotherhood, most notably by anti-Muslim figurehead Frank Gaffney.

And while Gaffney’s theories were once relegated to the fringe of American politics, they now carry real currency in a Trump White House with deep ties to anti-Muslim hate groups.

A terror designation would make it illegal for anyone in the U.S. to provide “material support or resources” to or be “otherwise associated with” the brotherhood, allowing the Trump administration to target groups like CAIR and ISNA.

This would enable the government to conduct warrantless searches and to seize the assets of these organizations over the course of yearslong investigations, effectively shutting the groups down. As Thursday’s letter states, the government wouldn’t even require proof that CAIR and ISNA had “actual intent or knowledge of wrongdoing” to prosecute them.

“As a result, the potential negative impact on American Muslim civil society of false and unjust smears and investigation resulting from a terrorism designation of the Muslim Brotherhood is high,” the letter states.

The destruction of these Muslim groups, the letter contends, could leave American Muslims vulnerable to persecution.

“Muslim civil rights groups work to protect communities against discriminatory laws and policies,” it says, “a role that is critical at a time when the threat of anti-Muslim measures is extraordinarily high and hate crimes against those perceived as Muslim have soared.”

The Muslim Brotherhood, which counts millions of members across the Middle East, renounced violence decades ago, and won elections in Egypt after President Hosni Mubarak was deposed during the Arab Spring in 2011. In 2013, the group fell into disarray after Egyptian President Mohamed Morsi, a brotherhood member, was deposed.

Thursday’s letter marks the most comprehensive and organized opposition to date against Trump’s reported plan to designate the Muslim Brotherhood a terror organization.

Foreign policy and counterterror experts across the political spectrum have vocally opposed the designation. And the editorial boards of both The New York Times and The Washington Post have also come out against it. Last year, an investigation by the U.K. government determined that the brotherhood is not a terrorist organization.

There is literally not a single U.S. expert on the Muslim Brotherhood that I'm aware of who supports designating it as a terrorist group — Shadi Hamid (@shadihamid) February 9, 2017

Aside from the designation’s implications for American Muslim groups, experts have noted that it might also be illegal for the U.S. to designate a terror organization on solely ideological grounds, without evidence that it is actively committing or plotting terror attacks.

Moreover, experts have argued that the designation would not only deeply disrupt U.S. relations with Middle Eastern allies where the brotherhood or its offshoots hold some level of power, but could also increase terrorism itself.

Politico obtained a CIA memo last month noting that the terrorist designation would “fuel” extremism in the Middle East.

The designation “would probably weaken” brotherhood leaders’ arguments against violence “and provide ISIS and al-Qaeda additional grist for propaganda to win followers and support, particularly for attacks against U.S. interests,” the memo said.

The White House did not immediately respond to a request for comment on the civil rights’ groups letter against the Muslim Brotherhood terror designation.

You can read the full letter below: