In the history of the Communist Party of the Soviet Union the Left-Right bloc was a failed attempt of vocal opposition to the politics of forced collectivization Joseph Stalin. Vissarion Lominadze and Sergey Syrtsov were recognized as its leaders. The name is derived from the accusation in factionism of the group created by joining of two groups: the one accused in "right opportunism" and allegedly headed by Syrtsov and another one accused of "lefism" and "half-Trotskyism" allegedly headed by Lominadze. In Western literature the case is known as the Syrtsov-Lominadze Affair.
The issue was part on the agenda of the November 4, 1930 joint session of the Bureau of the Moscow Committee of the RKP(b) and the Presidium of the Central Control Commission which considered the issue, "On the Factional Work of Comrades Syrtsov, Lominadze, Shatskin and Others." The resolution of the session declared, in part, that Syrtsov had "organized an underground factional center which included Nusinov, Kavraiskii, Galperin, Kurs, and others" and that Lominadze had "headed a persevered fractional group which included Shatskin, Reznik, and others."
There are opinions that in fact there was no such bloc, that while the dissenting views were public indeed, the whole affair was fabricated. E.g., Roy Medvedev expressed an opinion that Stalin learned some details of a conversation between Syrtsov and Lominadze.
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.