Annual European Police Congress in Berlin
The former head of the German Federal Office for the Protection of the Constitution (Bundesamt fuer Verfassungsschutz) Hans-Georg Maassen attends the annual European Police Congress in Berlin, Germany, February 4, 2020. Reuters

Once he was Germany's top Nazi hunter. Now the conservative opposition want to kick former domestic security chief Hans-Georg Maassen out of their party for allegedly repeating anti-Semitic and racist tropes.

Until 2018, Maassen headed the Federal Office for the Protection of the Constitution, chasing down extremist threats to Germany's constitutional order, whether from foreign spies, religious fundamentalists, the far right or the far left.

But the long-time member and one-time parliamentary candidate of former Chancellor Angela Merkel's Christian Democrats (CDU) lost that job after being accused of ignoring video evidence of far-right gangs chasing immigrants in riots.

Now, after Maassen mused in an interview about "a green-leftist race theory" that casts "whites as inferior" and promotes "immigration by Arabic and African men", the CDU have lost patience with a man who kept doubling down on culture war tropes, making himself a cult figure on the right fringes.

"He keeps using language from the world of anti-Semites and conspiracy theorists, even ethnic supremacist terminology," the CDU presidency said in a statement on Monday, giving him a deadline of Sunday to leave the party or face expulsion.

Maassen criticised the announcement in comments to the conservative newspaper Die Welt. "What I said wasn't racist, but what many people think," he said. "I reject ideological positions that demand the extinction of 'whitebreads' - those with white skin colour - through mass immigration."

The decision to eject Maassen four years after he first became notorious highlights the dilemma facing the CDU, which has a slim lead in polls over Chancellor Olaf Scholz's Social Democrats and the Greens, but which risks shedding voters to the far-right opposition Alternative for Germany.

New CDU leader Friedrich Merz has charted a more right-wing path for the party than the famously centrist Merkel, criticising government plans for a more generous immigration and citizenship policy as "devaluing" German citizenship.

If Maassen fails to quit, expulsion could be a long process. Under German party democracy laws introduced to prevent the re-emergence of dictatorial parties like Hitler's Nazis, expulsion can only follow a series of quasi-judicial hearings to establish whether a member is in conflict with the party's values.

Maassen told Die Welt there was no legal basis to expel him.