Russia's State Duma has ratified the treaty on the Eurasian Economic Union (EES).
Russian lawmakers unanimously supported the treaty, calling it "historic," at their session on September 26.
The EES was established on the basis of a customs union by the presidents of its member states -- Russia, Belarus, and Kazakhstan -- in Astana on May 29.
It is scheduled to officially start functioning from January 1, 2015.
Moscow has been pressuring former Soviet republics to join its customs union and the EES, saying the latter will be modeled after the European Union.
Armenian Prime Minister Ovik Abramian said earlier in July that an agreement allowing his country to join the EES will be signed by the end of October.
Kyrgyz President Almazbek Atambaev has said that Kyrgyzstan will join the customs union by the end of 2014.
Based on reporting by Interfax and ITAR-TASS