German Chancellor Olaf Scholz called on the Polish government Saturday to clarify allegations about a cash-for-visas deal for migrants that has roiled Polish politics, as a debate about immigration heats up in Germany.

The demand from Scholz marks stepped-up rhetoric from Poland’s powerful western neighbor, coming just days after sources said Germany summoned the Polish ambassador and Interior Minister Nancy Faeser spoke to her Polish counterpart on the topic.

Since earlier this month, the Polish government has been facing accusations by opposition parties that it was complicit in a system in which migrants received Polish visas at an accelerated pace without proper checks after paying intermediaries.

Arrivals to Poland could easily cross into other European Union countries given that borders are open.

Poland’s government has written to the European Union’s security commissioner to say that the scandal was an exaggerated “media fact” timed to discredit the ruling nationalists in a tough battle for re-election next month.

“The visa scandal that is taking place in Poland needs to be clarified,” Scholz said on Saturday at an event. “I don’t want people from Poland to simply be waved through.”

Scholz hinted that Germany could take steps to control the border with Poland.

In recent years, Germany has already coped with floods of migrants and asylum seekers from Syria and Ukraine.

In a letter to Polish Foreign Minister Zbigniew Rau, EU Commissioner for Home Affairs Ylva Johansson demanded full clarification of the scandal of up to 350,000 purchased work visas for the EU-Schengen area, BILD reported this week.

In the letter made available to BILD, the commissioner points out that the behavior of the Polish authorities could mean “a violation of EU law and in particular of the EU Visa Code.”