Hardliners of Chancellor Angela Merkel’s conservative bloc are poised Monday to give the German leader an ultimatum to tighten asylum rules or risk pitching the country into a political crisis.

Three years after her decision to open Germany’s borders to migrants fleeing war in Syria and Iraq and misery elsewhere, Merkel is still struggling to find a sustainable solution to end the grumbling from her Bavarian allies CSU over her liberal refugee policy.

Monday is “destiny day for Angela Merkel. For the government,” wrote the mass-circulation newspaper Bild on Sunday.

Interior Minister Horst Seehofer of the CSU has been one of the fiercest critics of Merkel’s liberal stance that allowed a million asylum seekers into Germany since 2015.

The interior minister now wants to turn away at the border new arrivals who have previously been registered in another EU country — often their first port of call, Italy or Greece.

But Merkel is firmly opposed, warning that it would leave countries at the EU’s geographic southern periphery alone to deal with the migrant influx. Instead, she wants to find a common European solution at the June 28-29 EU summit.

Popular misgivings over the massive migrant influx have given populist and anti-immigration forces a boost across several European nations, including Italy and Austria where far-right parties are now sharing power.

In Germany, voters handed Merkel her poorest score in September’s elections while giving seats for the first time to the far-right anti-Islam AfD.

Several high profile crimes by migrants — including the 2016 Christmas market attack by a failed Tunisian asylum seeker as well as the recent rape-murder of a teenage girl allegedly by an Iraqi — have also helped to fuel anger.

The case of a German teenager who was believed to have been stabbed to death in a supermarket by her Afghan asylum seeker boyfriend is due to be heard in court on Monday.

With an eye on October’s Bavaria state election, the CSU is anxious to assure voters that it has a roadmap to curb the migrant influx.

Seehofer’s “masterplan” on immigration was meant to be the showpiece of the CSU’s tough stance against new arrivals.

But the interior minister was forced to cancel a planned presentation of his vision after Merkel disagreed with his proposal to turn some asylum seekers away at the borders, sparking last week’s dramatic escalation of discord within the conservative bloc.

For all the noise, the CSU knows that there is more at stake.

Seehofer struck a more conciliatory tone when he told Bild on Sunday that “it is not in the CSU’s interest to topple the chancellor, to dissolve the CDU-CSU union or to break up the coalition.

“We just want to finally have a sustainable solution to send refugees back to the borders.”

Seehofer’s CSU party is due to meet Monday to decide which course to take.

He has the nuclear option of seeking approval to shut Germany’s borders immediately in defiance of Merkel, or the less aggressive choice of giving her an ultimatum of two weeks to sort out a deal with other EU nations.

Signalling that he is leaning towards the latter option, Seehofer wrote in a column in Frankfurter Allgemeine Zeitung that “it is essential that the EU summit takes a decision at the end of June.

“The situation is serious but still solvable,” he wrote.

Whichever option he chooses, the ball will land in Merkel’s court.