My pregnant wife has been asked to resign

My wife has worked for her company 6 years as a regular casual, pretty much full time hours for the past 4 years. She went full time in September 2024 and has received her letter the she has passed her 6 month probation. She is due in September and when she told her work she is pregnant they said to her she has to resign. She asked for a document or a piece of writing where it states that but her work isn’t giving any written evidence stating that she has to resign. She is very stressed out at the moment doesn’t know how to go about the situation. Is this legal to be told to resign because you are pregnant?