Work is a central source of identity and meaning. The rapid and widespread adoption of generative artificial intelligence (GenAI) is reshaping workplaces. Unlike previous technologies, GenAI can demonstrate cognitive, creative, and interpersonal capabilities that challenge traditional human-machine boundaries and redefine the knowledge, task, and social characteristics of work. GenAI can benefit workers by enhancing their productivity and performance. It can also psychologically threaten workers' needs for competence, autonomy, and relatedness, which can initiate five coping strategies to mitigate these threats. We unpack the effects of GenAI on work and workers, show the importance of addressing its potential psychological threats, and explain how to foster human-centered workplaces that balance the benefits and risks of GenAI.