There are six months left of Angela Merkel's third administration, and it apparently still has a few things on its plate to finish up, particularly when it comes to tightening asylum laws. One related issue is closing a perceived loophole that allows hard-up German men to sell their paternity to foreign women so that a child can gain German citizenship - and the child's mother can gain residency.

Read more: Record rise in babies with foreign mothers in Germany

The proposal was just one bullet point on the summary that emerged from a recent coalition committee meeting, where politicians from the parties in the current coalition met to set out their remaining agenda, and it did not go beyond a bald declaration: the Interior and Justice Ministries would be "commissioned to agree on a draft law in the short term" that would "prevent acknowledgement of paternity to improve residency rights."

Read more: Coalition partners butt heads, shake hands in all-night coalition meeting

Though acknowledging paternity does theoretically oblige a man to pay for the upkeep of children, if he is without means, this makes no practical difference. 

The idea is not new. The German parliament passed a similar law during Merkel's first tenure in 2008 that allowed authorities to challenge a paternity claim when they suspected fraud - which they could do if the supposed parents weren't married or the supposed father had never lived with the child.

The German Constitutional Court eventually scrapped this law six years later. It ruled that the law represented a violation of parental rights, since there are plenty of legitimate reasons why a man might claim the paternity of a child he hadn't fathered. Not only that, there is a constitutional bar against withdrawing German citizenship from someone once it has been granted.

At the time of the ruling, refugees' rights organizations like Pro Asyl welcomed the court's decision, arguing that the law had created a "culture of suspicion" in migrant law that forced people to prove they had a relationship with their children. The organization also called on the government not to try to re-frame the law, and for almost three years the government turned its attention elsewhere.

Clear fraud?

It is not clear how often such abuse cases might occur; the Interior Ministry would only say that there was an "increasing number," and since authorities have not been allowed to challenge paternity since 2014, few cases have arisen.

Markus Roscher-Meinel, a Berlin-based lawyer who specializes in family law, called the problem "modest" in practice, not least because once a man claims paternity for a child and the mother agrees, the matter is essentially settled from a legal point of view.

It was, he said, therefore always basically speculative for authorities to subsequently challenge paternity claims. "How are the authorities supposed to find out if a man was paid?" he wondered. "The Constitutional Court said that if the authorities investigate, they have to have concrete suspicions, and these have to be named in the law so as not breach people's rights."

"Men have acknowledged 'cuckoo children' for completely honorable reasons - because they can't have children and are glad to have children in the family, or because they looked the other way so as not to endanger their marriage - all these reasons are protected in an article in the Basic Law," he added, referring to Germany's constitutional document. "It's a very complex situation."

Read more: German plan would make mothers reveal child's biological father

A thousand problems

But family lawyer Eva Becker said that doesn't mean making a new law would be pointless. She remembered cases reported in the media of men claiming the paternity of several hundred children. "There probably aren't many cases," she told DW. "But if you have ten men who each acknowledge a hundred children, then you have a thousand problems. It doesn't need to be many to make a problem out of this situation, and make it worthwhile to be regulated legally."

At the same time, Becker also agreed that the Constitutional Court's objections to the law were legitimate. "The authorities could then test any child it wanted to see if the relationship existed or not," she said. "That really wouldn't be possible."

The German government consequently now faces a legal question: how do you formulate the idea of "concrete suspicion of fraud" in the law to avoid impinging on personal rights?

"The authorities can't write the criteria for a suspicion of fraud into the law preemptively," said Becker. "You'd have to write in exactly what the authority needs to show to challenge paternity - for example if the authority finds out that a father has acknowledged the paternity of a hundred children. Three or four children would also be enough, if the authority can prove that the father has never had a relationship with them."