When Norway was invaded by Germany in April 1940, Lie immediately started organising resistance, taking charge of free radio broadcasts from various locations in the country. For two months this work kept him in constant movement around Norway, and on 7 June 1940, when King Haakon VII and the government left the country for London, he was in Vadsø, replacing a broken transmitter. At this point further broadcasts became impossible, and Lie had to make his way south, through Finland and Sweden, to Oslo. Here he became involved in the underground labour movement, mainly through printing newspapers and spreading information.