"Millions in Soviet Donate A Day's Work to Country", by Theodore Shabad, The New York Times, April 18, 1971, p1 https://www.nytimes.com/1971/04/18/archives/millions-in-soviet-donate-a-days-work-to-country-soviet-workers.html
"Riga Subbotnik". Retrieved 2008-09-14. http://rigadailyphoto.blogspot.com/2008/09/liela-talka.html
Kaplan (1968) p.359
"Millions in Soviet Donate A Day's Work to Country", by Theodore Shabad, The New York Times, April 18, 1971, p1 https://www.nytimes.com/1971/04/18/archives/millions-in-soviet-donate-a-days-work-to-country-soviet-workers.html