Despite the disagreement in 1908, Heftye and Knudsen were not estranged. Knudsen would later sit as Prime Minister from 1913 to 1920, and he used Heftye as an arbitrator in both the national wages board and in irregular labour conflicts. Previously, during his time as telegraph director, Heftye had started the institution of non-legal wiretapping—a method which was later used in labour conflicts. He was also an international arbitrator from 1919 to 1920 when he sat on the Slesvig Commission, preparing the partition into Northern and Southern Slesvig in 1920.