The agreement on establishing the customs union was signed by the presidents of Russia, Belarus and Kazakhstan in Dushanbe, Tajikistan in October 2007.

"At a plenary meeting, the members of the Senate adopted the law ’On the ratification of the agreement on establishing a joint customs zone and forming a customs union’," the spokesman said.

The document is to be later signed by Kazakh President Nursultan Nazarbayev, RIA Novosti reported.

The three other members of Eurasec - Tajikistan, Uzbekistan and Kyrgyzstan - will also be able to join the customs union.