The Union of European Turkish Democrats had been due to hold one rally later Thursday in the western town of Gaggenau, with Turkey's Justice Minister Bekir Bozdag as the guest speaker.
But Gaggenau authorities withdrew an earlier agreement for the group to rent a hall for the event, saying it did not have the capacity to host so many people.
"Because the event is now known across the region, the city expects a large number of visitors. However, the Bad Rotenfels hall, parking lots and access road are insufficient to meet that demand," the town's authorities said in a statement.
"Due to these reasons, the hall rental agreement with the UETD has been revoked," it added.
Separately, Cologne city authorities said they would no longer allow the UETD to use a hall on Sunday, when Turkish Economy Minister Nihat Zeybekci is expected to make a rally speech.
"The event can and will not happen there," a spokeswoman for Cologne city authorities told AFP.
It was unclear if Zeybekci would be able to find an alternative site.
The UETD had earlier reserved a room in the city hall of the Cologne-Porz district for a "theatre event", said the spokeswoman.
But on Wednesday, the group said it would now host an "information event".
The city said however that it would no longer make the site available to the group, citing difficulties in guaranteeing security at such short notice.
Turkish politicians including Prime Minister Binali Yildirim have sparked controversy over their visits to Germany to hold political rallies.
Germany is home to about three million people of Turkish origin, the legacy of a massive "guest worker" programme in the 1960s and 70s and the biggest population of Turks in the world outside of Turkey.
And Erdogan's government is keen to harness their votes for the April 16th referendum, which would discard the post of prime minister for the first time in Turkey's history.
Critics say the new presidential system will cement one-man rule in the country.
Berlin-Ankara relations have been strained by a series of disputes since the failed coup that aimed to oust Erdogan last July.
The latest issue dogging ties is Ankara's provisional detention of a German journalist on terrorism-related charges.
Deniz Yucel, 43, a correspondent of the German newspaper Die Welt, has been held since February 18th in connection with news reports on an attack by hackers against the email account of Turkey's energy minister.
Berlin's sharp criticism of Ankara's massive crackdown after the failed putsch has also irked Turkey.