Author Paul Kengor has uncovered several documents in the Soviet archives showing that, in the 1930s, the American Civil Liberties Union was not at all unfriendly towards Stalin. From [1]:

Kengor found a May 23, 1931 letter in the archives signed by ACLU founder Roger Baldwin, written on ACLU stationery, to then American Communist Party Chairman William Z. Foster asking him to help ACLU Chairman Harry Ward with his then-upcoming trip to Stalin’s Russia.

The letter suggests Ward intended to visit the Soviet Union to find “evidence from Soviet Russia” that would undermine the capitalist profit motive.

Baldwin wrote the letter at a time when Stalin was deporting 1.8 million Ukrainian peasants to Siberia under his policy of the forced collectivization of agriculture, which resulted in the deaths of up to 10 million Ukrainians in the two years that followed [the Holodomor genocide].

...Foster was a key figure in the early years of the American communist movement who belonged to the ACLU’s National Committee in the 1920s, according to FBI documents. He later wrote a book titled “Toward Soviet America” in 1932 and also testified under oath before Congress that he opposed American democracy.

Another letter on ACLU letterhead Kengor found in the Soviet archives dated Sept. 2, 1932 asks the [USSR-controlled] Communist Party of America for a schedule of Foster’s trips around the country and offers to help keep the police at bay. It also asks for the names and addresses of Communist Party representatives in the cities where Foster was speaking.

Kengor also found a flier from 1933 advertising ACLU board member Corliss Lamont as the headline speaker for “Soviet Union Day,” which its organizers hoped would “answer lies and slanders of enemies of the Soviet Union.”...

That doesn't mean that the ACLU is currently a Communist organization, but it might be helpful for their supporters to compare the above to the whitewashed version at aclu.org/aclu-history .

And, whatever they did in the 30s, the way to oppose them now is over their very strong support for illegal immigration and their direct link to the Mexican government. See their name's link at the start of this post for background information and some questions you can ask their leaders.

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[1] dailycaller . com/2011/01/04/the-aclu%E2%80%99s-untold-stalinist-heritage