But you can also hear that the USSR was ready for war and had been a war economy since the Civil War and never converted their factories back to civilian use, they continued to mass produce tanks/weapons and they were anxious for a war against Romania and change the status quo.
At that time, Soviets have held their elite troops on the far east, in expecting of an attack from Japanese. So Stalin wanted to do everything to avoid war with Germany at that time, because his western border was less protected. That was the moment Hitler decided to attack. It took Soviets months to transport their troops from the far east, but luckily on time to defend Moscow.
Regarding Romania, it was just Hitler's fear Soviets could have occupied their oil facilities. But since Stalin wanted to avoid war with Germany at that time, he certainly wouldn't have attacked Romania in order not to provoke Germany on war.