The right-wing Alternative for Germany (AfD) reprimanded a party member on Monday for using neo-Nazi slogans on a messaging service, saying it damaged the party's image before the country's September election.
The AfD made big electoral gains last year, capitalizing on fears about Chancellor Angela Merkel's open-door policy toward migrants but its support has roughly halved in the past 12 months due partly to a slowdown in refugee arrivals.
The party has also been dogged by an internal power struggle and disagreements over how to deal with members who have used neo-Nazi language or adopted some arguments put forward by the ultra-rightist National Democratic Party (NPD).
Andre Poggenburg, AfD head in the eastern state of Saxony Anhalt, shocked many Germans by sending messages in a WhatsApp group of AfD members saying "Germany for the Germans," a slogan often used by the NPD.
Poggenburg has acknowledged the comments, and last week sent a tweet saying, "Why could this put pressure on me? Of course 'Germany belongs to the Germans' and it should remain so."
In a warning to Poggenburg, the AfD party board said the comments "massively damaged the image of the party in an election year," according to a spokesman.
The board also cited comments in the chat group about expanding Germany's borders which, it said, gave the impression of "pushing the party toward right-wing radicalism."
Germany lost eastern territory to Poland and Russia when the Nazi regime was defeated in World War Two, something that fringe far rightists in Germany have never accepted.
In January, the AfD disciplined Bjoern Hoecke, the party's chief in the eastern state of Thuringia, for criticizing the Holocaust Memorial in Berlin, but they stopped short of expelling him.
Also hanging over the party is an attempt by prosecutors to lift the parliamentary immunity of AfD leader Frauke Petry as part of a perjury investigation over statements she gave about the financing of the AfD's 2014 Saxony state election campaign.
Three months before a federal election, the AfD are polling at about 7-8 percent in most surveys, raising the possibility among some commentators that they even may fail to win the 5 percent needed to enter the Bundestag Lower House.
Want to enjoy 'Zen' reading - with no ads and just the article? Subscribe todaySubscribe now