Turkish media reported on Friday that German-Turkish citizens in the German city of Brühl received unsigned letters threatening them if they do not leave the country.
The letter in German -- widely shared on social media -- targets what it calls supporters of President Recep Tayyip Erdoğan, who became a loathed figure in Germany when he openly criticized Berlin for embracing supporters of terrorism.
The letter attacked Turkish expats who backed the constitutional changes which were also advocated by Erdoğan.
"Do yourself and your president a favor, and return to your country," the letter read, claiming that those who voted in favor of the presidential system in the April 16 referendum were not well-integrated into Germany.
"We are worried about supporters of Erdoğan in Germany. They cannot be allowed to live with us. They should take their families with them and leave Germany," the letter continued. It said Turks should leave "for their own good."
It is not clear whether German police launched an investigation into the anonymous letters.
Halis Özdoğan, a German citizen of Turkish origin who has been living in the country since 1974, told Anadolu Agency that the letter left the families in shock.
"The message to us here is that 'either you will be like us, or you will leave the county'. This is frightening, this is unacceptable," he said.
Özdoğan said such prejudices and generalizations about Turkish expats were not true, and was a sign of growing racism.
Germany is home to nearly 3 million Turkish immigrants, and Turkey's April 16 referendum was widely debated in the country.
On Sunday, more than 50 percent of Turkish citizens voted 'Yes' to a presidential system. In Germany, the 'Yes' campaign had received stronger support.
Among the 700,000 Turkish expats who casted their ballots in election centers across Germany, 63 percent of them voted in favor of a presidential system in Turkey, while 39 percent voted against.
German politicians who backed the 'No' campaign argued that big support for Erdoğan and his proposal for a presidential system among the expats was a sign that they were not well-integrated.
Several far-right politicians also called on Turks who backed the 'Yes' campaign to leave Europe and return to Turkey.
Turkish community leaders have sharply criticized such calls and warned against growing racism in Germany.