Angela Merkel's conservatives accused their coalition partner on Monday of a "massive breach of trust" in backing opposition candidate Joachim Gauck for the German presidency, a move which forced the chancellor to support him despite deep reservations.
Germany's Bild newspaper said Merkel's centre-right government had even come close to collapsing during tense negotiations on Sunday evening between her and Free Democrat (FDP) leader Philipp Roesler over who should fill the largely ceremonial post.
According to the paper, Merkel warned Roesler that he was putting the coalition at risk by backing Gauck, a former rights activist in East Germany whose candidacy the chancellor publicly opposed less than two years ago.
"Is that what you really want?" the paper quoted Merkel as saying.
Roesler reportedly refused to budge and an hour later Merkel's Christian Democrats (CDU) and their Christian Social Union (CSU) sister party, caved in and reluctantly agreed to back Gauck, who was nominated by the opposition Social Democrats (SPD) and Greens.
Reuters could not immediately confirm the details of the reported exchange, but members of Merkel's party reacted furiously on Monday to the FDP's stance.
Michael Kretschmer, a lawmaker from Merkel's CDU, spoke of a "massive breach of trust" by the FDP that would have serious consequences for future cooperation. Bavarian Finance Minister Markus Soeder of the CSU accused the FDP of "extortion" in comments reported by Bild.
A senior member of the FDP who requested anonymity told Reuters the talks had been "on a knife's edge."
The FDP, which has slumped in opinion pulls to between 2 and 3 percent, has been pushed around by the conservatives many times in the last two years but seems to have reached their limit in the Gauck affair.
If Merkel had not backed down and agreed to support Gauck, she would have faced a fight with opposition parties and within her coalition that might have become a major distraction in the midst of the euro zone debt crisis.
Gauck, 72, now seems sure to succeed Christian Wulff, Merkel's hand-picked choice for president in 2010 who resigned on Friday in a scandal involving financial favors.
She pushed through his election at the time despite the fact many Germans and the leading opposition parties wanted Gauck to become president.
Gauck, a Protestant pastor, was a leading figure in the peaceful protest movement that led to the fall of the Berlin Wall. He was one of a number of pastors who supported the protests that ultimately brought down the East German regime, setting the stage for the reunification of Germany in 1990.
After the Berlin Wall fell, Gauck ran the state-run archives on the Stasi, earning recognition for exposing the crimes of the dreaded East German secret police.
While the president has no power over policy, the person in the role has been seen as a source of moral guidance and can influence the political debate by giving speeches.
(Additional reporting by Andreas Rinke and Thorsten Severin)