BERLIN—German Chancellor Angela Merkel’s ruling conservatives are holding last-ditch talks this weekend to defuse an escalating dispute over immigration and avert a breakup of her government.
Horst Seehofer, who is Ms. Merkel’s interior minister and a party leader in her fragile coalition, has threatened to ignore a veto by the chancellor and forge ahead next week with a plan to turn away some migrants at the German border.
Doing so would effectively hand the chancellor an ultimatum: Fire Mr. Seehofer, which would fracture the coalition and prompt new elections just under 100 days after the government was sworn into office; or give in to his demands and see her authority further diminished.
Signalling the level of concern in Ms. Merkel’s circle, a conservative cabinet minister told The Wall Street Journal on Friday that such an unprecedented show of defiance by a member of a government would likely lead to the collapse of Ms. Merkel’s alliance.
Mr. Seehofer and his party said he would start implementing his controversial plan on Monday, even without approval from the chancellor.
The row is pitting Ms. Merkel’s Christian Democratic Union against the Christian Social Union, its sister party in the southern state of Bavaria, which Mr. Seehofer leads. The two have long shared a parliamentary group, acting as a single party on the national stage. They rule together in a fragile alliance of staunch conservatives, centrists and left-leaning Social Democrats, all with diverging views on immigration.
But Mr. Seehofer’s CSU has grown increasingly estranged from Ms. Merkel since her decision to open Germany to hundreds of thousands of asylum seekers in the summer of 2015.
The influx has since abated but the political tension it triggered has refused to go away.
The anti-immigration Alternative for Germany, which was created in 2013 and polled in the low single digits for years, is now the biggest opposition party in parliament. An Infratest Dimap poll published on Thursday gave AfD 15% of voter support, 2½ points above its September election result.
Mr. Seehofer’s CSU is particularly concerned about a state election in Bavaria this October. A poll by Civey this month showed that the party could lose its absolute majority, dropping to around 41% of the vote as the AfD becomes the second-biggest party with 13.5%.
Immigration policy has also reshaped political landscapes elsewhere in Europe, at times dramatically so, and strained relations between European Union members. In Austria, Chancellor Sebastian Kurz has moved to tighten immigration and reduce benefits available to asylum seekers since he took office in December.
On Wednesday, Mr. Kurz joined Mr. Seehofer in a Berlin press conference and called for an “axis of the willing” to combat illegal migration between Austria, Italy and Germany—the countries along the main route for irregular migrants crossing the Mediterranean.
Italy’s new populist government, which has taken a hard line on asylum, has also signaled support for Mr. Seehofer. Rome prompted international condemnation this week by closing Italian ports to the Aquarius, a French ship that carried over 600 migrants rescued at sea. French President Emmanuel Macron said the Italian government had acted with “cynicism and irresponsibility.”
Mr. Macron himself, has been no exception to the trend, announcing tighter immigration laws this year. Sweden, long Europe’s most welcoming country for refugees, has all but closed its borders.
The sudden escalation in Berlin came as a surprise this week. Mr. Seehofer had been due to present a 63-point immigration plan on Tuesday when he canceled the event because of a dispute with Ms. Merkel.
At issue is a single measure that would give German border police authority to turn back anyone entering the country illegally if they have no identity documents or are found to have previously requested asylum in a different EU country.
Ms. Merkel and her supporters argue that the initiative would alienate Germany’s neighbors just as she is trying to engineer a pan-European approach to asylum and refugees.
Mr. Seehofer argues that the move is compliant with international law and would only prevent people with no prospect of obtaining asylum from entering Germany.
After almost a week of talks there was no sign of compromise by Friday evening. Mr. Seehofer and the CSU said they would start implementing the plan next week, deploying police along the border with Austria. The party has said that if Mr. Seehofer loses the interior minister post it would pull out of the government.
In a sign of acrimony, legislators from the CDU and the CSU met separately in parliament for the first time. Ms. Merkel asked her party to wait until after a summit of EU leaders on June 28, so she could hammer out bilateral deals with countries who would take back migrants rejected by Germany, according to lawmakers who attended the meeting.
“I believe that we should not act unilaterally, we should not act in an uncoordinated manner and we should not act to the detriment of other countries,” Ms. Merkel said Thursday.
Rejecting asylum seekers at the German border could trigger a domino-effect and jeopardize European integration, Annegret Kramp-Karrenbauer, secretary-general of Ms. Merkel’s CDU and widely seen as her preferred successor, wrote in an email to all party members this week.
Hinting at possible divisions within Ms. Merkel’s own party, Ms. Kramp-Karrenbauer exhorted party members to back the chancellor against Mr. Seehofer.
Mr. Seehofer countered in an interview with the Süddeutsche Zeitung daily published on Friday that it was the CDU and Ms. Merkel that had divided Europe by opening German borders to refugees in 2015.
Under EU rules, immigrants must apply for asylum in the country where they first enter the bloc. Currently, all asylum seekers are allowed to stay in Germany pending the review of their applications.
“Relations between the sister parties have never been this bad and the government is now hanging by a thread,” said Robin Alexander, a journalist who wrote a book about the 2015 refugee crisis.
The arrival of 1.4 million people since 2015 has turned politics in what had long been one of Europe’s most stable countries upside down. While Ms. Merkel won September’s election, she scored her party’s worst result since 1949 and took more than six months to form a government.
Crimes committed by migrants—including rapes, killings and terrorist attacks—have kept the issue in the news, as have allegations of mismanagement and corruption at Germany’s migration agency. And while the flow of arrivals is sharply down from three years ago, some 10,000 people still enter the country illegally every month, according to government estimates.
An Infratest Dimap poll for public-sector broadcaster ARD conducted earlier this week found that 62% of Germans supported turning back some migrants at the border, while 86% backed more robust deportations of rejected asylum seekers; 63% said they weren’t satisfied with the work of the coalition.