We have been told that we are not allowed to provide resources in Spanish to our Spanish speaking students because it would be unfair for students who speak other languages. Is this accurate?

You cannot deny students something that would be academically appropriate and beneficial for them in the name of equality. If you have resources in Spanish, then provide them to students who could benefit from them. Of course, the district should strive to provide native language resources to as many of their students as possible, but it is inappropriate to deny any students these resources until you can provide them to all students.