Renate Kuenast, the parliamentary co-leader of the Greens, said on Monday her party planned to present legislation in parliament that would outlaw the kind of questioning used by the conservative-led government in the southwestern state of Baden-Wuerttemberg.
"A country governed by law cannot ask questions about moral values," Kuenast told The Associated Press in Stuttgart. Potential citizens can be asked only to respect the law, she said.
Starting on 1 January, officials have been given a list of 30 questions to be used as guidelines during interviews with Muslims who are applying for German citizenship.
Possible questions include probing applicants' opinions on homosexuality and how young women should dress.
"Imagine that your grown up son comes to you and explains that he is homosexual and would like to live with another man. How would you feel?" reads one question.
The list has been sharply criticized by Muslim groups and lawmakers, as well as Jewish leaders, who argue it is discriminatory.
But state officials in Baden-Wuerttemberg have defended the list as a fair way to assess whether future citizens uphold the values guaranteed by Germany's constitution.
Baden-Wuerttemberg Governor Guenther Oettinger's coalition of conservatives and pro-business Free Democrats faces a state election in late March.