If the employer is subject to FMLA, then the answer appears to be yes.
From an internet search: Employers who are subject to FMLA are:
- Public agencies, including local, state, and federal employers, and local education agencies (schools), regardless of the number of employees.
- Private sector employers who employ 50 or more employees for at least 20 workweeks in the current or preceding calendar year, including joint employers and successors of covered employers.
From another internet search: Employers are required to maintain group health benefits for employees who take FMLA leave. However, employers don’t have to pick up the whole tab unless that is their regular practice. If the employee was required to pay their share of insurance premiums prior to going on FMLA leave, they are required to continue paying their share of insurance premiums while on FMLA leave. If the applicable insurance premiums increase or decrease while an employee is on FMLA leave, the employee is required to pay the new insurance premiums.
If the group is not subject to FMLA and an employee drops below 30 hours (or the required minimum in the state), then the employer does not have to cover their premium, but the employee should be termed and go on state continuation (if it’s not a COBRA group) during the time they don’t meet the coverage requirements.