Why do you think the Soviet Union opposed the Marshall Plan?
Their opposition has to be seen in the context of international politics at the time.
The Marshall Plan was, from a Western perspective an economic strategy to use American aid in order to regenerate the economies of Europe. Such regeneration was seen as necessary in the immediate aftermath of World War 2, given the level of devastation the war had caused.
The Soviet Union opposed on ideological grounds. Stalin saw it as an attempt to impose capitalism on Europe thus undermining the socialist system in the Soviet Union, and in those East European countries which had become or were in the process of becoming Soviet satellite states.
He also saw it in terms of realpolitik, namely as part of an attempt by the USA to achieve global hegemony as the two superpowers emerged from World War 2.
Europe had already been largely divided up at a series of wartime conferences for example Yalta,Potsdam and Casablanca. However it was still the case that the situation was fluid and both superpowers sought to gain advantage as the new Cold War began to be played out in Europe.
Stalin also opposed it because of the Soviet Union's experiences during World War 2 and before that. 3 times in the previous 31 years they had been attacked by the West with devastating consequences, particularly Operation Barbarossa in 1941.
The Marshall Plan was seen as part of a strategy to contain Soviet influence and specifically regenerate Germany into a Western alliance. Given the fact that the Soviet Union lost an estimated 27 million people as a result of the Nazi invasion, Stalin had good reason to be wary.