In the Second World War, Portuguese Jews tried to emphasize their Portuguese origin by obtaining a place on Portuguese and emigration lists in order to prevent deportation. This is what archive assistant Lydia Hagoort puts in “Het Beth Haim in Ouderkerk aan de Amstel”, a history of Beth Haim, the cemetery of the Portuguese Jews in Amsterdam.
By means of extensive pedigree and scientific research, the Portuguese Jews tried to show that they belonged to the Mediterranean and not to the Jewish race. Their Jewish identity would only be based on religion. In this way, they could not only obtain a place on a Portuguese list, which could save them from deportation, but also end up on an emigration list, which would make migration to Portugal possible.
Eventually, it was decided from the German side that the Portuguese were indeed Jews, and so the large majority ended up in extermination camps
Source: Historisch Nieuwsblad (translated from that Dutch website)