If this is the same person (and time and place align), Wiernik was also busy in the 1930s writing subversive materials out of a Jewish charity organization.
Gazeta Powszechna from August 17, 1935 has an article titled "Communist Party Headquarters Under Lock and Key: 66 Subversives Arrested in Warsaw."
A secret printing press was discovered underneath the shop of a shoemaker named Rosenberg.
In total, over 100 searches were carried out, 66 people were arrested, and a huge amount of a huge amount of propaganda materials, leaflets, brochures and books in Russian, Polish, French, English and Yiddish, and a large amount of correspondence and proclamations from the central committee were also taken for the files. Lists, notes, receipts and account books were also found. Copiers, printing equipment, office supplies and three typewriters were also found, which were used to make wax copies for copiers and carbon copies. ...
A search was conducted at the Jewish charity institution ‘Dom Chleba’ (13 Elektoralna Street) and two typewriters were found on which Jankiel Wiernik, an employee of the ‘innocent’ Dom Chleba, wrote proclamations on carbon paper, which were read during the investigation.
Among the 66 arrested are prominent communists who had been conducting subversive work within the central communist party authorities for a long time.
Gazeta Polska has more info on the investigation from August 8, 1935.
The communist authorities in the capital uncovered a perfectly secret communist printing house, obviously run by Jews. It printed all the communist periodicals, such as "Czerwony Sztandar," "Nowy Przegląd," etc., as well as brochures, leaflets, and proclamations.
...
Subversive literature was being smuggled out en masse across the country.
I didn't want to derail the Treblinka plagiarism thread, but these OCR Polish newspaper archives are a goldmine.