Ultimately, the employer is responsible for providing appropriate controls (up to and including PPE if needed) and training employees follow procedures and use PPE effectively. That is true whether the PPE is provided by the employer or by the employee. Employers should have a program and policy in place around the provision of PPE. If an employee is using PPE that requires fit testing or maintenance, the employer is responsible for providing the necessary training. Employees should also understand how the PPE fits into the hierarchy of controls and protocols in place in the plant to protect workers. Employers may make the decision not to allow employees to provide their own PPE if they cannot be confident that it's quality PPE and in good condition.
Some workers are opting to wear Cloth and Surgical masks. It is important to make aware that these types of masks may not protect you from the virus. These do not form a tight seal with the face and are not considered as an equivalent to the N95s. Cloth and surgical masks have their limitations, and these should be communicated to your workers. See this document from WorkSafeBC, on the differences between Cloth, Surgical, and Disposable N95 respirators.