As the frontline of our education system, teachers endure greater job-related stress than other professionals, even under the best of circumstances. While they were already exposed to certain stressors affecting their emotional health, the pandemic outbreak introduced new challenges putting teachers at risk of experiencing higher rates of emotional distress. This longitudinal study aimed to identify changes in teaching stressors and teachers’ coping strategies in the period before the pandemic to the immediate outbreaks of COVID-19 in Fall 2020. In addition, we examined the correlation of teachers’ coping approaches with stress, anxiety, and depression to understand if coping strategies correlate and predict such emotional distress. To this end, 376 English as a foreign language (EFL) teachers in Iran in the first wave and 351 in the second wave completed a battery of validated inventories capturing their emotional distress, teaching stressors, and coping approaches. The mean scores of the stressors and coping strategies across two waves indicated significant shifts toward using functional coping strategies upon experiencing new demands. Furthermore, we found that novice teachers experienced higher rates of stress and anxiety, which were positively associated with dysfunctional coping strategies. The results of the stepwise regression analysis with (dys)functional coping strategies indicated that coping mechanisms significantly account for 25% of variances in stress, anxiety, and depression. The implications of the study regarding promoting teacher mental health through identifying the risk factors associated with dysfunctional coping strategies have been discussed.