The massive service industry trade union Verdi said it would oppose the plans to cut what could turn out to be as much as 15 percent of the workforce.
"Our aim is to limit the job cuts as much as possible," said a Verdi spokesman.
The Frankfurter Allgemeine Zeitung and the Wall Street Journal said anywhere between 4,000 and 6,500 jobs could be in danger as the partly state-owned bank tries to reorganise. It has refused to comment on the reported numbers.
Talks are due to start with workers' councils next month.
Talk of massive job cuts surfaced in November, before the bank announced a major effort to cut costs and focus on core and profitable sectors.
Commerzbank chief executive Martin Blessing said at the time it was clear that deep cuts in personnel costs would be inevitable, but declined to specify how much in savings would be made or how many jobs would be cut.
The bank returned to profit in the third quarter of 2012, booking a net profit of €78 million compared with a loss of €687 million in July through September 2011.
The result fell short of analysts' expectations, however.