I can't remember the exact wording, but I'm pretty sure they can't do that. I have recently retired from Nursing and I know that pregnant staff were not allowed to work nights on health grounds - and that was without any complicating factors as employers have a duty of care. Maternity Benefit (or whatever they are calling it these days) is payable from the 28th week of pregnancy and it is the individual mother's choice as to whether or not she wishes to continue to work after that point. Twenty eight weeks used to be the earliest age of viability for the baby, (it is now 22 weeks) and it is also one of the more important landmarks of the pregnancy as it is around this time that PIH (Pregnancy Induced Hypertension) can raise its ugly head. She should talk to Occupational Health and also, equally importantly, to her Union Representative.