Background: Besides major employment disruptions, the COVID-19 pandemic has generated policy responses with specific mechanisms to protect workers' health. In Belgium, most of these policies were negotiated at national and cross-sectorial level but implemented at company level with company-based collective negotiation playing a key role. This study examines the relationship between trade union representatives' perception of social dialogue quality and change in workers' physical and mental health in such a context. Methods: Union representatives were surveyed throughout Belgium between August and December 2021 through an online questionnaire (N=469). We asked about the way they perceived workers' physical and mental health within their companies and explain variations with the self-perceived change in quality of social dialogue as an exposure. We use a modified Poisson regression for binary outcomes on four stratified models that additively account for no control, company characteristics, pre-pandemic self-reported health and COVID-19-related measures. Weights are generated to ensure sector representativeness. Results: 30.1% of the sample reported a worsening social dialogue quality during the pandemic. Relative Risks (RR) of poor physical and mental health when social dialogue has worsened are respectively 1.49 [95%CI:1.03; 2.15] and 1.38 [95%CI= 1.09;1.74] when controlling for company characteristics and pre-pandemic health. Adding pandemic-related measures reduces the risk of both poor mental [RR=1.25; 95%CI: 0.84; 1.87] and physical health [RR=1.18; 95%CI:0.94;1.49]. Conclusions: Although based on self-reported variables, the study shows an association between poor social dialogue quality and poor physical and mental health during the COVID-19 pandemic that must be explored further in post-pandemic context.