In July-August 1936 Luzin was criticised in Pravda, notably for publishing his best papers in western journals and only minor ones in the USSR. Other accusations include holding reactionary ideas and claiming other's work as his own. After the series of articles, Soviet mathematicians published papers only rarely abroad.
Nikolai Nikolaevich Luzin (http://www-history.mcs.st-andrews.ac.uk/Mathematicians/Luzin.html) and The case of Academician Nikolai Nikolaevich Luzin (http://www-history.mcs.st-andrews.ac.uk/Miscellaneous/other_links/Luzin.html)
Luzin's school was at its peak during the years 1922 to 1926, but then Luzin concentrated on writing his second monograph on the theory of functions and spent less time with the young mathematicians in the school.
The aim was obviously to get rid of Luzin as a representative of the old pre-Soviet mathematical school of Moscow: his master, Egorov, had been himself the victim of such a campaign in 1930 (based on his religious sympathies) and died shortly after in 1931 in despair and misery.
Luzin always had an interest in the history of mathematics and late in his career he wrote important articles on Newton and on Euler.
Kolman attacked Luzin in print, associating him with Egorov and other reactionaries, and alleged that he was tainted with Fascism; this denunciation prevented Luzin from going to the international congress at Zurich in 1932.
The attack on Luzin began after he was asked to report on some school tests, and reported in an invited article in Izvestiya on 27 June 1936 that he found the standard surprisingly high.
Luzin made a statement, promising to take account of the criticisms, and to publish primarily in the Soviet Union; his statement was received with understanding and sympathy.