He continued working for the ITF, although the federation insisted that he put forward more centrist views in this role, and eventually required him to resign from the OSP, returning to the SDAP.
He established an underground network of sailors based in the country, and planned to remain in Amsterdam to further this activity even once it became clear that World War II was imminent.
As leader of the ITF, Oldenbroek served on the Extraordinary Advisory Council of the Dutch government-in-exile, and joined the board of directors of the International Labour Organization.
However, he became concerned that the largely communist leadership of the WFTU did not share the interests of the whole movement, and so became a leading figure in the split which formed the International Confederation of Free Trade Unions (ICFTU).
This came to a head in 1960, when Meany argued for the ICFTU to adopt a top-down approach to trade unionism in Africa, while Oldenbroek wished local activists to take the lead.