After the outbreak of the war, Olszyna-Wilczyński's unit was to prepare the defense of the area between Biebrza River, Suwałki, and Wizna. However, due to German breakthrough in Lesser Poland the Operational Group was disbanded and its units withdrawn to Lwów, where they later took part in the battle for that city. Olszyna-Wilczyński himself escorted his units to Pińsk, where he met with Marshal of Poland Edward Rydz-Śmigły. After the Soviet Union invaded Poland on 17 September, the Polish government issued orders to its military that they should avoid fighting with Soviet forces. Nonetheless both pro-Communist rebels (Skidel rebellion) and various Soviet units did not shy away from attacking Polish units.