No. An employee on FMLA leave is entitled to have health benefits maintained while on leave as if the employee had continued to work instead of taking the leave. 29 CFR 825.100(b). This doesn't mean that an employer can't change the insurance under any circumstances. If, for instance, the employer is changing insurance plans for all employees, it would not violate the FMLA for the insurance of an employee on FMLA leave to be changed at the same time as all the other employees.
If your rights under the FMLA have been violated or if you have questions about those rights, contact Lexington, Kentucky FMLA and employment lawyer Robert Abell at 859-254-7076.