Austrian Chancellor Christian Kern has proposed a ban on Turkish politicians’ campaigning in the European Union, but Turkish Economy Minister Nihat Zeybekci is still reportedly planning to visit Turkish voters in Germany.

In an interview with the German newspaper Welt am Sonntag, Kern said that Europe should protect its individual member nations from Turkish President Recep Tayyip Erdogan‘s drive to win over expatriate Turks ahead of April’s Turkish referendum on boosting his constitutional powers.

“A joint approach by the EU to prevent such campaign appearances would be sensible,” Kern said.

As reported by Deutsche Welle (DW), Germany’s international broadcaster, the latest strains in EU-Turkish relations centre on Ankara’s arrest of German-Turkish journalist Deniz Yucel and rejections on security grounds by the German towns of Guggenau, and Frechen near Cologne, of gatherings at which visiting Turkish ministers were to have made campaign appearances.

According to Kern, Erdogan’s plan for “the introduction of a presidential system would further weaken the constitutional state, constrain the separation of powers and contradict the values of the European Union.”

He also demanded Ankara immediately free the German-Turkish correspondent of the conservative German newspaper Die Welt, as well as numerous other journalists and scientists detained since last year’s coup attempt in Turkey.

On March 3, Erdogan accused Yucel of being a “German agent” and supporting the armed Kurdistan Workers’ Party (PKK) through his reporting.

In a separate report, the Middle East Eye online reported that several German towns recently prevented appearances by Erdogan’s ministers, citing security and safety concerns.

The cancellations have angered the Turkish government, which accused Berlin of seeking to undermine its referendum campaign.

German Foreign Minister Sigmar Gabriel said on March 5 in a guest article for newspaper Bild am Sonntag that Berlin would “certainly not end our criticism of developments in Turkey”.

Gabriel insisted Germany would stand up for the rule of law, freedom of opinion, human rights and democracy.