Sahra Wagenknecht is a prominent member of the Linke party, which was meeting in Magdeburg when the attack took place on Saturday.
The 46-year-old leader has sought a limit on the number of refugees Germany should accept, which has put her at odds with others in her party.
A group calling itself Anti-Fascist Initiative “Cake for Misanthropists” distributed flyers, pointing to her position on migrants as their motive.
Photos taken after the attack showed the smartly-dressed leader covered in chocolate icing and crumbs.
The influx of over one million migrants, mostly Muslims, into Germany last year has hardened German public opinion on immigration and pushed the government to toughen asylum rules
PTI