In the history of the Communist Party of the Soviet Union the Left-Right bloc (Russian: лево-правый блок, romanized: levo-pravyy blok) was a failed attempt of vocal opposition to the politics of forced collectivization Joseph Stalin.
E.g., Roy Medvedev expressed an opinion that Stalin learned some details of a conversation between Syrtsov and Lominadze.
[2] Pierre Broué wrote that Medvedev was wrong and there was indeed a bloc, because some of Trotsky's letters mentioned a real oppositional group between Lominadze, Jan Sten and Syrtsov.
[5] Robert Davies notes that the case was part of the overall 1930 campaign against dissent (actual or potential) within the party.
Davies also notes a peculiarity that unlike many other cases of Soviet political suppression, the campaign against Syrtsov and Lominadze in press did not associate them with "wreckers", nor with "imperialist forces" abroad.