Is it legal in the state of New Jersey to not allow students from 6th grade an up to change clothes for gym class?

When i was in 5th grade i began changing clothes for gym and was told it was a law that i had to do so. Now, 8 years later, my sister is in 8th grade with a new principal who decided to change the rules that they are not allowed to change for gym. All the students complain that they do not want play gym with out changing because of hygene purposes. I was wondering if it is legal to not allow the students to change before and after physical activity in gym class?