The vote during the CDU party conference signals the party's intention to reverse a compromise that the CDU agreed to with its coalition government partner the Social Democrats (SPD) in 2014.
The CDU and SPD agreed to change the law as of December 2014 to allow immigrant children to keep both German citizenship and that of their parents.
The reform entails certain requirements for those who want to maintain their dual citizenship, such as showing proof that they had lived in Germany for eight years, or attended a German school for at least six years.
Previously children born to foreign parents from certain countries were allowed to have dual citizenship up until the age of 23, but then had to choose which nationality they would keep.
But Merkel herself criticized her party's vote to undo the reform.
“We should not go back on this law,” Merkel told broadcaster N-tv.
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