The field of language policy and planning has seen increasing scholarly attention that explores social actors' micro language planning towards a given language policy situation at the grassroots level. In educational contexts, teachers and educators are often considered pivotal locals whose agency, when enacted in micro language planning, can contribute to educational language policymaking. However, little attention has been given to learners -- those on the receiving end of educational language policy. Situated in the current discourse concerning Mandarin-dominated Chinese language education, within the context of China's promotion of Mandarin language learning, this study examines dialect-background heritage learners in a tertiary-level Mandarin Chinese language programme in New Zealand. By adopting the concept of micro language planning, this study explores how dialect-background heritage learners perceive and react in a Mandarin-dominated Chinese programme. The findings show that dialect-background learners exercise agency to interpret, implement, reject, and negotiate language policy according to their self-identified language needs. However, their ability to enact agency is also constrained by a series of social realities including socio-economic discourse, language ideology, language proficiency, and technology development. This study offers implications for language policy makers involved with different levels of Chinese language policy.