Change in Compensation Maternity

I have a friend who is pregnant and is about to go on maternity leave. Her
boss has told her that before she goes on maternity leave her payment status
is going to be modified from that of a salary based compensation structure
to a commission based compensation structure. Although she has no ideas
about maternity laws she feels as if the boss is doing this at a weird time.
Is there any benefit to the company for doing this? Will my friend be hurt
by this in any way, loss of money, loss of health benefits, better ability
to sever her employment? Is what her employer doing illegal in any way? Can
an employer modify a job from salary to commission if the job was accepted
as a salary position? It seems as if that is unfair and the employee should
have some recourse. I may be wrong but it seems similar in a way to
modifying a contract. Although I understand New Jersey is an at will
employment state it just seems wrong to me for an employer to just take your
salary away especially when your about to take a federally/state protected
health leave. Please help if you can. I apologize if I am grossly ignorant
of the law and have used wrong terms or assumptions.

Best regards,

Jason Norton