It was well known that Poland wanted to invade USSR, with help of Nazi Germany. Felix Dzerzhinsky presented the following report:
The possibility of an armed attack on the Soviet Union from Poland, Romania and the Baltic border countries, under the influence and with the support of capitalistic England, is now becoming more and more relevant and from theoretical assumptions has transferred to the sphere of real opportunity.
Polish-source reports did much the same:
The dismemberment of Russia is at the heart of Polish politics in the east, so our possible position will be reduced to the following formula - who will take part in this dismemberment? Poland should not remain passive in this great moment of history.. The aim is to prepare well in advance both physically and spiritually. The main objective is the weakening and defeat of Russia.
Also, the Pildulski-Hitler pact stated that Poland would "actively cooperate" with Nazi Germany. They invaded Czechslovakia together,
Memoir of Ribbentrop with conversation with Beck (Polish ambassador):
Then I again spoke with Beck about policy of Poland and Germany against the Soviet Union and therefore also on the Great Ukraine, I again offered cooperation between Poland and Germany in this field.
Mr. Beck did not hide the fact that Poland claims the right to Soviet Ukraine and access to the Black Sea; he immediately pointed to the alleged dangers that, according to the Polish party, could arise from Polish treaty with Germany against the Soviet Union.