"After the recent debate about campaign appearances of Turkish government officials in Germany, Saarland will ban such appearances," the southwestern region said in a statement.
Turkey has been waging a war of words with its NATO partner Germany, with President Recep Tayyip Erdogan accusing it of "Nazi practices" after several German towns blocked rallies by Turkish ministers campaigning in favour of the referendum to expand the president's powers.
Erdogan has been seeking to harness the Turkish diaspora vote, which numbers as many as 1.4 million in Germany alone.
Facing an election in her own state later this month, Saarland premier Annegret Kramp-Karrenbauer said she would make use of a law allowing foreign officials' campaigning to be banned "when the peaceful coexistence of Germans and foreigners is threatened".
"Internal Turkish conflicts have no place in Germany," Kramp-Karrenbauer said.
"Election rallies that jeopardize the domestic peace should be outlawed."
Chancellor Angela Merkel has resisted calls for a general German ban on such campaign events.
But Kramp-Karrenbauer said Saarland, one of Germany's 16 federal states, would not wait until Berlin or even the European Union settled on an official policy on such events and would immediately implement its own ban.
"We here in Saarland have no problem with certain people but rather with their message. Our liberal democracy is not a haven from which to promote undemocratic goals," she said, referring to the referendum that some critics say would lead to one-man rule in Turkey.
But she said she hoped the policy would set a precedent "for the EU as a whole".