ChatGPT, a prominent Large Language Model (LLM) renowned for its capacity to facilitate real-time interactive conversations in natural language, has become increasingly prevalent in providing customer services in e-commerce platforms. This study examines the influence of ChatGPT-empowered product recommendation on the norm of reciprocity, reflected by characteristics of eWOM in the context of online travel agencies (OTAs). Drawing upon the reciprocity theory, we propose several hypotheses concerning the impact of ChatGPT-empowerment on anticipation-based and gratitude-based reciprocal behaviors, reflected in review quantity and quality. Leveraging a natural experiment conducted on leading OTAs (Expedia and Booking.com) and the unique panel dataset of online reviews for a matched set of hotels across both platforms, we employ a difference-in-difference (DID) model to assess the impact of ChatGPT-empowerment on online reviews. We find that ChatGPT-empowered product recommendations decreased the review quantity and quality (cognitive effort), evidenced by a reduction in the use of cognitive and abstractive languages, as well as a decreased complexity in review contents. Furthermore, we find a more pronounced impact on reviews stemming from positive consumption experiences compared to negative ones, reflected in review valences. To further delve into the underlying mechanism, we extensively assess measures derived from review contents reflecting norm of reciprocity among customers (prosocial behavior, fulfillment, and affiliation). Considering the potential risks associated with the negative effects, this study proposes an effective short-term measure leveraging social influence.