The answer to this question depends on a few factors, including the size of the employer and the number of employees.
Under the Affordable Care Act (ACA), employers with 50 or more full-time equivalent (FTE) employees are required to provide health insurance to their employees or face a penalty. However, this requirement has been suspended until January 1, 2021.
Small employers (those with fewer than 50 FTEs) are not required to provide health insurance to their employees, but may do so if they choose.
Part-time employees are not counted when determining whether an employer is required to provide health insurance.
You can read more about the ACA's employer mandate here: https://www.healthcare.gov/employers/