Background: The emergence of the COVID-19 pandemic has had major consequences in the workplace, both in terms of the number of cases among the working population and the enormous changes made to cope with it. The objective of this study is to describe the impact of COVID-19 on the working conditions and health of wage-earners in Spain. Methods: Cross-sectional study carried out between the end of April and the end of May 2020 among the wage-earning population. Sample included n = 20,328 participants obtained through an online survey. Results: A situation of high-strain was reported by 44.3% of workers, 42.6% were concerned about possible job loss, 75.6% about finding a new job if they lost the present one, 69.7% were worried about salary reduction, 68% about becoming infected at work and 72.3% of being a transmitter of the virus. Among those who regularly went to work, 13.1% did so with symptoms compatible with COVID-19 and 71.2% stated that they had done so without adequate protection measures. 36.7% of workers believe that their health worsened, 41.6% had severe trouble sleeping during the last month, 55.1% were at risk of poor mental health and consumption more than doubled of tranquilisers and opioid analgesics, compared to the pre-pandemic situation. Conclusion: The impact of COVID-19 on the wage-earning population has been enormous, with high exposures to harmful working conditions and very poor health indicators, which, compared to the pre-pandemic situation, means significant deterioration. Important inequalities are observed according to class, gender, age and wage.