Turnout among the 1.4m German voters with a Turkish background is expected to fall in the upcoming election after comments made by President Erdogan.
More than a third of the voters with Turkish roots are intending not to vote in the election, according to a survey.
Relations between Turkey and Germany have worsened since Mr Erdogan’s has launched a staunch effort to suppress opponents following the failed coup of July 2016. As more than 250 military and diplomatic figures have claimed asylum in Germany, a dozen German citizens have been arrested in Turkey.
In August, Mr Erdogan called on Turks in Germany to vote against major parties when the polls open on September 24.
“I am calling on all my countrymen in Germany: the Christian Democrats, SDP, the Green Party are all enemies of Turkey. Support those political parties who are not enemies of Turkey,”
Mr Erdogan urged ethnic Turks in Germany to “teach a lesson” to those parties.
German chancellor Angela Merkel and her election rival Martin Schulz both pledged to put an end to Turkey’s plans to join the European Union.
Turkey began formal accession talks to join the EU in 2005, however, negotiations were halted in 2016 amid criticism of Mr Erdogan’s behaviour.
Usually most German-Turkish voters support the Social Democratic Party (SPD). If the boycott goes ahead, Mrs Merkel’s Christian Democratic Union (CDU) would be likely to benefit most.
Just 44 per cent of German-Turks said that they were certain to vote, with 38 per cent saying they would not and 18 per cent undecided.
The survey of more than 1,000 voters was conducted by the Istanbul-based Turkish-European Foundation for Education and Scientific Studies (Tavak).
In the 2013 election 30 per cent did not vote, in line with the national turnout of 71.5 per cent.