BERLIN — Members of Germany’s center-left Social Democrats aired differences Tuesday over whether to renew their governing coalition with conservative Chancellor Angela Merkel, while the right of migrants to bring relatives to Germany resurfaced as a potential sticking point.

A party congress will decide this week whether to talk with Merkel’s Union bloc about extending the coalition of the past four years, or at least supporting a minority government. Merkel’s talks with two smaller parties collapsed last month, prompting a change of course by Social Democrat leaders — who after a disastrous election defeat in September had previously insisted they would go into opposition.

The “grand coalition” of Germany’s biggest parties is unpopular with many Social Democrats, and leader Martin Schulz has promised a membership ballot on any coalition deal.

Michael Roth, a deputy foreign minister, argued that the Social Democrats should enter a new coalition for the sake of efforts to reform the European Union, championed by French President Emmanuel Macron. Merkel’s bloc, he argued in an article in the daily Frankfurter Allgemeine Zeitung, doesn’t want “far-reaching institutional reform.”

“Only if Germany’s role as the reform motor in the EU is agreed in binding and concrete form in a coalition deal can this succeed — but not in the framework of parliamentary support agreements” for a minority government, he added.

The head of the Social Democrats’ youth wing, meanwhile, renewed a call to rule out entering a “grand coalition.”

Kevin Kuehnert, in an interview with ZDF television, pointed to “examples that show why we consider this ‘grand coalition’ the wrong idea, because the positions are so far apart” — among them the question of migrants’ relatives.

The left-leaning Greens’ call for relatives to be allowed to join people granted protection that falls short of asylum was one difficult point in Merkel’s previous coalition talks, although it appeared on track to be resolved and didn’t in itself sink the effort. The Social Democrats also want migrants’ families to be allowed to come.

But senior conservative Horst Seehofer told Tuesday’s Bild daily he “cannot imagine” agreeing, saying it would lead to “massive immigration.”