German Chancellor Angela Merkel says she respects local leaders’ decisions to cancel Turkish political rallies, despite Turkish government anger.
There was a bomb scare at the town hall in Gaggenau after officials withdrew permission for Turkish Justice Minister Bekir Bozdag to address a rally. Police found no bomb, so the alarm was lifted.
Cologne has prevented another Turkish minister from speaking at an event.
The constitutional changes would boost Mr Erdogan’s presidency and significantly weaken parliament’s role.
A spokeswoman for Chancellor Merkel said Germany wanted to lead by example on issues of freedom of speech and opinion.
Despite the Cologne restriction, Turkish Economy Minister Nihat Zeybekci vowed to visit the city anyway on Sunday and meet ethnic Turks face-to-face.
“If we see that they still don’t give us permission, I’ll go from coffee house to coffee house, from house to house, to meet our citizens anyway,” he said.
The row is troubling for Chancellor Merkel because she persuaded Turkey to help block the surge of migrants – many of them Syrian refugees – into the EU.
Crackdown on opposition
In Turkey, dozens of writers and journalists have been arrested in a far-reaching crackdown that followed a failed coup against Mr Erdogan in July 2016.
The authorities have purged the police, schools and other public services of alleged supporters of Fethullah Gulen, a US-based cleric blamed for the coup. He denies plotting against Mr Erdogan.
Turkey arrested a German-Turkish reporter last week, straining ties.
Deniz Yucel, who works for Die Welt, is accused of producing terrorist propaganda and undermining the Turkish government.
‘You are not Turkey’s boss’
Turkish Foreign Minister Mevlut Cavusoglu accused the German government of backing opposition to Mr Erdogan’s planned constitutional changes.
“If you want to maintain your relations with us, you have to learn how to behave. You cannot tackle these matters with these methods. It can’t go on this way. If necessary we will respond in every way. And then you can think about the rest. This is our message to Germany.”
Earlier, German Justice Minister Heiko Maas sent his Turkish counterpart, Mr Bozdag, a sharply-worded letter warning against “dismantling the rule of law”.
He said the Turkish treatment of Mr Yucel was “disproportionate”.
“If Turkey fails to uphold core European values, then closer relations with the European Union will become more difficult, or impossible,” he wrote.