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Refusing to allow part-time work may amount to discrimination
An employer's refusal to allow a woman to work part-time in connection with pregnancy or return from maternity leave may be found to be unlawful discrimination. The Anti-Discrimination (Carers' Responsibilities) Amendment Act 2000 (NSW) makes it unlawful to discriminate against an employee or job applicant on the ground of caring responsibilities.
(this is nsw rule, by the way... maybe u could look up what the legal requirement is in Qld.. its probably same or similar)