Both Employers and Employees are subject to Penalties:
Employers will be out of CMS Compliance if they fail to distribute and report Part D Creditable Coverage Notifications.
Employers and Employees may have to take contributions out of an HSA acccount if the employee has Medicare Part A.
Employees may have delayed Part B enrollments and monthly penalties if the employer is under 20 (Medicare Primary) and they have not signed up for Medicare Part B during their initial enrollment period.
Employees will be subject to a Part D late enrollment penalty (paid monthly for the rest of their life) if the company plan (any size company) is not Part D Creditable and they didn't sign up for Part D during their initial enrollment period.