This study investigates the application of AI to immigration authorities, which are faced with an overwhelming workload and fair decision-making tasks due to the increase in global immigration. We used mixed-methodology (discrete choice experiments and in-depth interviews) to explore the possibility of using large-scale language models (LLMs), such as GPT-3.5 and GPT-4, as decision-support tools in immigration adjudication. The results of the study show that LLMs can make decisions that are consistent with human decision-making strategies, emphasizing utility maximization and procedural fairness. However, ChatGPT showed limitations in that it showed stereotypes and biases about nationality, despite having safeguards to prevent unintentional discrimination, and showed preferences for certain groups. This shows both the potential and limitations of automating and improving immigration adjudication using LLMs.