Requirement of change rooms for ophthalmic/sterile plant

What is the requirement of change rooms in a sterile /ophthalmic plant .Which guidelines governs this .What are the recommendation made on the basis of study performed.

Pal 1 is class D
Pal 2 is class C
Pal 3 is class B
Pal 4 is class B

If I am an inspector inspecting a ppthalmic grade B facility. I wanted to go inside Grade B area, but was refused to do so unless I do the qualification programme as per the company’s policy and Sop of qualification of Gowning ( 3 days programme). Are they entitled to refuse entry