(ABC 6 News)- A federal appeals court in St. Paul heard opening arguments on Tuesday regarding an injunction that halts enforcement of a controversial “book banning” law that was scheduled to go into effect in Iowa last year.

Judge Stephen Locher issued a preliminary injunction last December, halting enforcement of the law before it was set to take effect Jan. 1 but already had resulted in the removal of hundreds of books from Iowa schools.

The law, passed and signed into law by Governor Kim Reynolds, bans books depicting sex acts from school libraries and classrooms and forbids teachers from raising gender identity and sexual orientation issues with students through the sixth grade.

The lawsuit argues the measure is unconstitutional because it violates students’ and teachers’ free speech and equal protection rights.