House conservatives on Friday called on the chamber's Ethics Committee to investigate Rep. Joaquin Castro Joaquin CastroPompeo accused of stumping for Trump ahead of election Florida Democrat asks FBI to investigate anti-Semitic, racist disinformation Hispanic Caucus members embark on 'virtual bus tour' with Biden campaign MORE (D-Texas) for tweeting the names of Trump campaign donors.

“Posting a target list of private citizens simply for supporting his political opponent is antithetical to our principles and serves to suppress the free speech and free association rights of Americans," the lawmakers wrote in a letter to House Ethics Committee Chairman Ted Deutch Theodore (Ted) Eliot DeutchShakespeare Theatre Company goes virtual for 'Will on the Hill...or Won't They?' Florida Democrat introduces bill to recognize Puerto Rico statehood referendum Matt Gaetz, Roger Stone back far-right activist Laura Loomer in congressional bid MORE (D-Fla.) and ranking member Rep. Kenny Marchant Kenny Ewell MarchantHouse Ethics panel recommends ,000 fine for Rep. Schweikert's campaign finance violations Candace Valenzuela wins Texas runoff to replace retiring Rep. Marchant Ethics Committee reviewing Rep. Sanford Bishop's campaign spending MORE (R-Texas).

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“These acts must immediately be investigated to determine if Rep. Castro has violated the ethical rules of this institution,” they added.

The letter spearheaded by Rep. Andy Biggs (R-Ariz.) was signed by GOP Reps. Matt Gaetz Matthew (Matt) GaetzTrump faces tricky choice on Supreme Court pick Florida attorney general scrutinizing Bloomberg paying fines for felons to vote Lara Trump campaigns with far-right activist candidate Laura Loomer in Florida MORE (Fla.), Jody Hice Jody Brownlow HicePelosi must go — the House is in dire need of new leadership House Republicans investigating California secretary of state's contract with Biden-linked firm GOP lawmakers want answers from Disney on Mulan, China MORE (Ga.), Debbie Lesko (Ariz.), Jeff Duncan Jeffrey (Jeff) Darren DuncanBiden's Iran policy is deeply flawed GOP lawmaker calls for Confederate portrait to be put back in Capitol Rep. Banks launches bid for RSC chairman MORE (S.C.), Randy Weber Randall (Randy) Keith WeberOVERNIGHT ENERGY: Cheney asks DOJ to probe environmental groups | Kudlow: 'No sector worse hurt than energy' during pandemic | Trump pledges 'no politics' in Pebble Mine review Cheney asks DOJ to probe environmental groups GOP's Gohmert introduces resolution that would ban the Democratic Party MORE (Texas) and Ted Budd Theodore (Ted) Paul BuddHouse Dems introduce bill to require masks on planes and in airports Bipartisan bill introduced to require TSA to take temperature checks How to combat substance abuse during COVID-19 MORE (N.C.).

The lawmakers argued that publishing donor lists suppresses free speech and the right to freely associate.

“By publishing a list of private citizens who donated to his political opponent, Rep. Castro sought to encourage harassment against those citizens simply on the basis of their political beliefs," they wrote. "It cannot be fairly argued that Rep. Castro had any other purpose in posting that list and telling his activist followers that those individuals were inciting hate. Whether he intended to provoke physical violence or merely verbal harassment, his intent was to chill the free speech and free association rights of Americans."

A spokeswoman for Castro dismissed the Republicans' request to the Ethics panel, calling it "baseless" and suggesting that "these Members of Congress know that."

"The information shared by Representative Castro is publicly available through the Federal Election Commission and the kind that’s routinely reported in media outlets of every political persuasion," Castro spokeswoman Katherine Schneider argued.

"Their letter is a disingenuous attempt by pro-dark money, far-right legislators to limit Americans’ ability to track money in politics. They would prefer large contributions to be kept secret so that there’s no meaningful transparency in political giving. We look forward to hearing from the Committee if the request is considered.”

Castro, the brother of Democratic presidential candidate Julián Castro, came under fire this week from House GOP leaders and President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE's campaign for tweeting the names and business interests of dozens of donors to Trump's reelection campaign.

On Monday evening, following that weekend's mass shooting in El Paso, Texas, Joaquin Castro tweeted the names of 44 Texans who donated the maximum $2,700 to Trump, specifically calling out the owners of several prominent businesses in San Antonio, where the Castro brothers are from.

Federal candidates are required to disclose the names and employers of donors who contribute $200 or more in Federal Election Commission filings, which are publicly available online.

However, it is unusual for a lawmaker to publish the names and business interests of individual donors of another campaign.

“Their contributions are fueling a campaign of hate that labels Hispanic immigrants as ‘invaders’,” Castro tweeted.

At the time, there were reports that the suspected gunman had allegedly posted a manifesto online shortly before the attack that included anti-immigrant rhetoric and warned of a “Hispanic invasion.”

The suspect has since reportedly told police that he carried out the shooting and that he was targeting "Mexicans."

Julián Castro defended the tweet after Trump blasted the move.

"Joaquin and I will keep fighting. The American people will fight every day for our nation, against your hate, your corruption, and your ego. And we’ll win. #AdiósTrump," he tweeted.

Updated: 7:05 p.m.