Germany's justice ministry has drawn up a change in the law which would require mothers in certain paternity cases to reveal who they had slept with.
The measure would apply when men who had supported a child, believing that they were the father, sought financial redress in court.
They could thus more easily claim maintenance back from the actual biological father.
Women would only have the right to remain silent with "serious reasons".
Justice Minister Heiko Maas said (in German): "We need to offer more legal protection for 'false' fathers to seek financial compensation".
The precise wording of the new paragraph states that the mother would be obliged to provide information to the man on "who has lain with her during the conception period".
Men in this situation were already able to try to claim back money paid for a child that was not theirs.
The draft change follows a ruling by Germany's highest court in March 2015 that there was no legal basis to force mothers of so-called "cuckoo children", in German slang, to name the biological father.
The draft changes, which will require parliamentary approval, also limit the "false" father's financial claim to two years' worth of maintenance costs. Previously this was open-ended.
A 2005 review of studies into so-called paternal discrepancy published in the British Medical Journal found that the rate was around 4% - meaning one in 25 children is biologically fathered by someone other than the man who believes he is the father.