In fact, at least some constitutional law theorists in Russia see the right of secession as a Confederation’s hallmark, not Federation’s one. And there is also an article in the Criminal Code of Russia which marks “call to secede” as a crime. read more
Technically a sovereign state can not secede, it did already by the very fact of its establishment. However, according to the said Agreement of 1994 Tatarstan legislative system is but a part of Russian. And in accordance with the Russian criminal code public calls for secession are deemed as criminal offense. read more