German Chancellor Angela Merkel's Bavarian allies, deepening a coalition rift over refugee policies, threatened on Tuesday to take her government to court
if their demand to stem the flow of asylum seekers is not met.
Horst Seehofer, leader of the Christian Social Union (CSU) "sister party" to Merkel's Christian Democrats (CDU), wants Merkel to set up centers on the Austrian frontier to speed up deportation of migrants deemed unqualified for political asylum.
The letter with the threat of court action was faxed to Merkel on Tuesday, the Bavarian chancellery said, and she had until Friday to respond before Seehofer would publish it.
Thomas Oppermann, parliamentary leader of the Social Democrats (SPD), Merkel's junior coalition partner in Berlin, called Seehofer's written threat an "announcement of the break within the coalition."
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"In order to govern, the CSU is not a prerequisite," Oppermann added. Merkel's coalition with the SPD would maintain its large majority in parliament even without the CSU, which governs in Bavaria, the main entry point for arriving migrants.
Germany took in 1.1 million asylum seekers last year, leading to calls across the political spectrum to take measures to slow the influx.
The CSU has also blamed the SPD for a standstill in implementing steps to cut the flow of arrivals, such as the suspension of family reunions.
Gerda Hasselfeldt, a senior member of the CSU, said she sometimes doubted the coalition partner's willingness to actually reduce the number of asylum seekers.
Seehofer said Monday he would "exhaust all political and legal means" to change the Berlin government's course.
But Merkel has resisted growing demands to cap the number of asylum seekers.
Instead she tried to convince other European countries to take in quotas of refugees, pushed for reception centers at Europe's external borders and advocated for a deal with Turkey to keep refugees from entering the bloc.
The government's inability to agree on joint measures in the refugee crisis has seen Germany's right-wing Alternative for Germany (AfD) party gain support over recent weeks.
The latest INSA poll, published by newspaper Bild on Tuesday, showed that 13 percent of German voters supported the anti-immigrant party — its highest level of support yet.
