The use of Artificial Intelligence (AI) programs such as ChatGPT by university students has puzzled educators around the world who relied on written assignments outside the classroom for both coursework and evaluation. Several studies have focused on how students use this tool, their perceptions, or how AI can enhance language learning or writing skills. This paper addresses a particular case where students were traditionally asked to write a motivation letter as a homework assignment in the context of an academic and professional English course. Participants of the study were 4th-year students in a Spanish telecommunications engineering school. Within the course English for Professional and Academic Communication, one unit covers job search and job interview, including how to write an effective cover letter. Given the teachers’ lack of knowledge regarding how students improve their texts using AI or if they simply submit work done by tools like ChatGPT, the decision was made not only to allow but also to encourage students to use this tool. The goal is to integrate the use of ChatGPT in written expression tasks in a controlled context in order to observe trends regarding its use and reach conclusions based on the data. In this specific case, as part of a broader study, we depart from the assignments submitted by 100 students, a pre and post-test and their comments within focus groups to examine their perceptions of the use of ChatGPT and the actual process of its practical application.