Employers have a duty to provide a safe working environment relative to the expected duties of the employee and the risks in the workplace. If employees run the risk of becoming infected at work because of the work they perform, the employer must provide personal protective equipment. However, they should follow the directive of public health authorities and the ministry of labour. As of March 21, 2020, public health authorities are not generally recommending personal protective equipment such as masks or gloves or any other physical protective devices except for the health sector workplaces.
As a result, unless the use of personal protective equipment, such as masks, is a condition of employment or otherwise required for the employee to safely perform their duties, you can refuse employees to wear a mask for example, in the workplace.
This position on the wearing of non-medical mask has changed since May 20, 2020. As Canadian federal, provincial and territorial governments carefully and gradually reopen their economies, those taking public transit, returning to work or going out shopping are being urged to continue to adhere to public health advice as to the best line of defence against COVID-19. One of the recommendations being put forward is to wear a non-surgical/medical face-covering in public where physical distancing is not possible, and that may include the workplace. For more read the following First Reference blog post.