Rival political factions have been locked in a bitter war of words ever since Mr Maasen, the head of domestic intelligence service the Federal Office for the Protection of the Constitution (BfV) contradicted Mrs Merkel over the veracity of a video appearing to show foreigners being attacked on the streets on Chemnitz by neo-Nazi extremists.
Chemnitz in the east of the country has been the scene of anti-migrant demonstrations by right-wingers in recent days, with one man handed a five-month jail salute for giving a Nazi salute.
Mrs Merkel had been convinced of the video, and cited it as an example as she condemned “hate on the streets”.
But Mr Maasen claimed the clip could be a forgery, despite offering no evidence to back this up.
His statement was later undermined by leaked police reports describing “100 hooded men” searching for foreigners, and an attack on a Jewish restaurant in the city.
The situation has been complicated still further by the revelation in the German Tageschau newspaper of a meeting between Mr Maasen and Stephan Brandner of the far-right Alternative for Germany (AfD) party earlier this year.
The Bild am Sonntag newspaper today said the BfV failed for months to act on reports from officials in two states voicing concerns about local youth chapters of the far-right AfD party.
The issue has split the coalition along party lines, with Mrs Merkel’s main coalition partner, the centre-Left Social Democrats (SPD) demanding Mr Maasen be axed from his job from they see as an attempt to interfere in politics.
However, he retains the backing of interior minister and leader of the Christian Social Union (CSU) Martin Seehofer – who forced a showdown with Mrs Merkel in July over his demands for tough new curbs on immigration.
SPD chairman Lars Klingbeil said: “It is absolutely clear to the SPD he must go.
“Merkel has to act now.”
Anton Hofreiter, co-leader of the Green Party’s parliamentary group, said: “If Mr Maasen sets out such claims, he must unequivocally prove them.
“Anything else would be irresponsible.”
“If Mr Maasen sets out such claims, he must unequivocally prove them. Anything else would be irresponsible.”
However, Mr Seehofer has publicly defended Mr Maasen, telling German newspaper Die Welt he saw no reason why he should lose his job.
The crisis is the latest act in what is proving to be a turbulent year for Mrs Merkel.
Apart from the run-in with Mr Seehofer, the SPD only agreed to join a coalition after a protracted period of soul-searching and considerable internal opposition which left Germany without a government for six months.
All parties are keen to keep her administration afloat, especially as recent opinion polls have shown the AfD party resurgent and poised to overhaul the SPD in terms of popular support.
Meanwhile, the scale of the crisis facing Germany has been highlighted by further demonstrations in Chemitz on Friday night.
Protesters were accused of setting out to harass foreigners in a city park on Friday night, with a 26-year-old Iranian man injured in clashes.
Police later arrested a group of 15 men aged 27-31, with nine eventually released, while six remain in custody.