A group of German leftists have posted online the names, addresses and telephone numbers of 2,000 Alternative for Germany (AfD) party members, Die Welt reported on Sunday.
Party spokesman Jorg Meuthen called the leak an act worthy of "criminal prosecution" which has caused considerable unrest among members, who are now in fear of "collective house calls" from left-wing activists, he said.
"We call on the federal government, specifically the federal Justice Minister Heiko Maas to carry out proceedings against radical left websites with the same intensity as he does radical right (wing websites)," Meuthen said.
The spokesman told Die Welt that the party leadership has instructed a legal firm to make a complaint to the public prosecutor in Stuttgart.
The party has not yet determined the source of the leak, but suspects it to have originated with the company employed by the party to manage its membership data.
