Turkey on Friday accused Germany of working for a 'No' vote in a referendum on President Recep Tayyip Erdogan's powers after the cancellation of several rallies. But Berlin has denied any role in the move.
Here's a look at what sparked the new spat:
What is the referendum about?
The Turkish public will vote on April 16th on whether to create a presidential system, which Ankara says will be like that in France or the United States and ensure political stability.
But critics say the system will further weaken parliament and herald a one-man rule by Erdogan, Turkey's strongman president.
Why is Turkey angry at Germany?
Ahead of the vote, Turkish politicians' trips to Germany have sparked controversy, notably a rally by Prime Minister Binali Yildirim in the western city of Oberhausen to garner support for a 'Yes' vote among the large Turkish community resident in Germany.
And on Thursday, several local authorities blocked rallies by two more Turkish ministers, prompting a furious response from Ankara which promptly summoned the German envoy to protest.
"They don't want Turkey to campaign here, they are working for a 'No'," Foreign Minister Mevlut Cavusoglu told reporters in the Turkish capital on Friday.
"They want to get in the way of a strong Turkey."
Cavusoglu accused German officials of failing to "honour democracy" and of allowing "terrorists" from the outlawed Kurdistan Workers' Party to speak but denying the same right to Erdogan.
The Turkish foreign minister warned Germany, which is facing elections later this year, it would "need to learn how to behave towards Turkey" if Berlin wanted to maintain ties.
"You must see us as an equal partner," he said.
Cologne city authorities withdrew permission on Thursday for the Union of European Turkish Democrats (UETD) to use a hall on Sunday for a speech by Economy Minister Nihat Zeybekci.
But Zeybekci said he would still go ahead with the visit.
"Even if they don't allow (it), I will go from house-to-house to meet with our citizens in Germany," he was quoted as saying by the state-run Anadolu news agency.
Is Germany really interfering?
Not according to the government in Berlin, which on Friday denied having anything to do with the municipal decisions to block the rallies.
"That is a decision the federal government has absolutely no influence on... because it falls under local or state jurisdiction on which we have zero influence," said foreign ministry spokesman Martin Schäfer.
Chancellor Angela Merkel also denied the charge on Friday, saying that the decisions to cancel the two rallies were "taken by municipalities, and as a matter of principle, we apply freedom of expression in Germany," she said.
"The referendum is a domestic issue for Turkey," Merkel's spokeswoman Ulrike Demmer said, adding: "Freedom of opinion... should be respected" both in Turkey and in Germany.
What is the spark for all this?
Politicians and activists in Germany have called for the government to ban Turkish politicians from speaking in Germany after a German journalist was jailed in Turkey on terrorism charges.
Deniz Yucel, 43, a correspondent for Germany's Die Welt daily, was charged with spreading terrorist propaganda and inciting hatred by an Istanbul court.
A dual national, he has been held in prison since February 18th. His apartment was searched in connection with news reports on an attack by hackers on the email account of Turkey's energy minister.
The minister, Berat Albayrak, is a son-in-law of Erdogan.
Despite considerable outrage in the German media at the arrest, the government has remained cooled, with Vice Chancellor Sigmar Gabriel only saying the case would make "everything harder" for Turkish-German relations.
Do Turkey and Germany ever get along these days?
It doesn't seem so.
Throughout 2016, Ankara was tossing verbal bombs at Berlin for one reason or another.
In April comedian Jan Böhmermann recited a poem on his popular late night show accusing Erdogan of having sex with goats and watching child pornography.
A furious Erdogan demanded that Merkel's government take action, leading the Chancellor to allow prosecutors to investigate Böhmermann for insulting a foreign head of state. The investigation was eventually dropped.
Then in June, the Bundestag (German parliament) passed a motion recognizing the mass killing of Armenians by the Ottoman empire during the First World War as a genocide.
Turkey responded by recalling its ambassador to Berlin and by banning German politicians from visiting German soldiers based at an airbase in southern Turkey.
That said, the countries are still heavily dependent on one another.
In early 2016 the EU, with Germany as the driving force, signed a refugee deal with Turkey, which pledged billion of euros in European support in return for Ankara preventing migrants from crossing the Aegean into the EU.