Turkey has summoned the German ambassador in Ankara to protest against the cancellation of a public speech by a Turkish minister in a German town.
Justice Minister Bekir Bozdag had been due to address expatriates in Gaggenau in support of President Recep Tayyip Erdogan's controversial reforms.
But local authorities withdrew permission for the rally, saying the planned venue was not big enough.
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.
Many Turkish writers and journalists have been arrested in a widespread crackdown that followed a failed coup against Mr Erdogan in July 2016.
The decision to summon the German envoy was made by Turkish Foreign Minister Mevlut Cavusoglu, Reuters said, quoting ministry sources.
Mr Bozdag has already cancelled his planned visit to Germany, where he had been also due to meet his German counterpart.
"It is unacceptable that German authorities, who constantly lecture us about human rights, democracy, rule of law, free speech... do not tolerate a meeting organised by the Turkish community," the Turkish minister said.
However, officials in Gaggenau, south-western Germany, said they had cancelled permission for the rally due to space considerations.
"Because the event is now known across the region, the city expects a large number of visitors," local authorities said in a statement.
"The Bad Rotenfels hall [in Gaggenau] parking lots and access road are insufficient to meet that demand."
Mr Bozdag had been expected to encourage the Turkish community in the western German town to support Mr Erdogan's controversial proposals to give greater powers to the presidency.
The Turkish authorities say the changes are needed to bring stability, while opponents say the reforms would cement one-man rule in the country.
Turkish citizens living abroad are eligible to vote in a referendum on the issue in April.
About three million people of Turkish origin currently live in Germany.