Chancellor Angela Merkel’s Bavarian allies have caused outrage by suggesting immigrant families that want to remain in the country should be obliged to speak German at home.

The Christian Social Union (CSU), sister party to Merkel’s conservatives and a partner in her government in Berlin, made the proposal in a draft policy paper due to be approved by CSU leaders today (8 December).

In the paper, the party says: “People who want to remain here on a permanent basis should be obliged to speak German in public and within the family.”

The proposal comes amid a sharp rise in immigration levels to Germany, driven by arrivals from eastern European Union members such as Poland, Romania and Bulgaria, as well as a surge in asylum seekers fleeing the war in Syria.

Back in October, leading Munich-based newspaper Sueddeutsche Zeitung reported that Bavaria could be forced to use tents from its annual Oktoberfest beer festival to house the large number of refugees.

Some members of the CSU are worried that the rise in immigrants will lead traditional supporters of the party to flee to the Alternative for Germany (AfD), a new extreme right party which preaches a tough line on immigration. The CSU was the driving force behind a new law earlier this year that clamps down on immigrants who abuse Germany’s generous social welfare system.

The CSU proposal on speaking German in the home was swiftly denounced by the other parties in Merkel’s government, including a senior official from the chancellor’s Christian Democratic Union (CDU).

“It is not the business of politicians whether I speak Latin, Klingon or Hessian at home,” Peter Tauber, general secretary of the CDU, said on Twitter.

Yasmin Fahimi, Tauber’s counterpart in the centre-left Social Democrats (SPD), who share power with Merkel, called the proposal “totally absurd”.

“The state has no role to play in deciding what language people speak within the walls of their own home,” Fahimi told right-wing German tabloid Bild.

Because of its ageing population and low birth rate, Germany desperately needs more immigrants to ward off a demographic crisis that poses a threat to the economy and state pension and healthcare systems. But many Germans are uncomfortable with the idea that their country is turning into a “melting pot” for foreigners seeking better jobs and lives.