According to an Amnesty press release from April:
On 8 April, the Russian Ministry of Justice delisted Amnesty International’s Moscow Office from the register of the representative offices of the international organizations and foreign NGOs, effectively closing it down alongside with offices of Human Rights Watch, Carnegie Endowment for International Peace, Friedrich Naumann Foundation for Freedom, Friedrich Ebert Foundation and other organizations. This decision has been taken “in connection with the discovered violations of the Russian legislation.”
On 11 March, Russia’s media regulator also blocked access to Amnesty International’s Russian-language website.
Has Russian authorities further detailed what "violations of the Russian legislation" that is about?