If there is a critical or time-sensitive matter that absolutely needs the employee's attention during their medical leave and if the matter directly relates to their position and there is no one else who can provide a suitable substitute, then it might be necessary for the employer to contact them. However, the employer should still keep the contact brief and minimize any unnecessary conversation related to work.
Employees should also be aware of their rights under the Family and Medical Leave Act (FMLA) or similar employment laws that provide protection during medical leave. If an employee feels their rights are being violated, they should consult with an attorney or relevant authorities to understand their options and seek appropriate legal recourse.