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)