Why is Russia concerned about former Soviet bloc countries being absorbed into the E.U?

EU expansion erodes Russia's sphere of influence. By joining the EU, former Soviet satellites gain the backing and support of the other countries in the EU, which have a combined population of 500 million people and approximatley 30% of the world GDP. Since Russia exerts control over its neighbours and satellites from a position of power (i.e. it is much bigger and wealthier) such tactics would no longer be effective against countries that joined the EU.