In 1940, after the German occupation, van der Veen was one of the few who re-fused to sign the so-called “Arierverklaring,” the Declaration of Aryan Ancestry. In the years that followed, he tried to help Jews both in practical and symbolic ways. Together with the musician Jan van Gilse and the (openly homosexual) artist, art historian, and critic Willem Arondeus, van der Veen established the underground organization De Vrije Kunstenaar (The Free Artist). Van der Veen and the other artists published a newsletter calling for resistance against the occupation. When the Germans introduced identity documents (Persoonsbewijzen) that distinguished between Jews and non-Jews, van der Veen, Arondeus and the printer Frans Duwaer (nl) produced some 80,000 false identity papers.