What was controversial about the revision of the german-soviet-polish borders.?

One of the most controversial matters addressed at the Potsdam Conference dealt with the revision of the German-Soviet-Polish borders and the expulsion of several million Germans from the disputed territories. In exchange for the territory it lost to the Soviet Union following the readjustment of the Soviet-Polish border, Poland received a large swath of German territory and began to deport the German residents of the territories in question, as did other nations that were host to large German minority populations. The negotiators at Potsdam were well-aware of the situation, and even though the British and Americans feared that a mass exodus of Germans into the western occupation zones would destabilize them, they took no action other than to declare that "any transfers that take place should be effected in an orderly and humane manner" and to request that the Poles, Czechs Slovaks and Hungarians temporarily suspend additional deportations.

they have different colored collars