Payroll US: Health Benefits are not deducted on FMLA absence

Hi,

An employee is on FMLA absence and gets no payment. But for ongoing calculation/deduction for health insurances (pre tax deductions) a bi weekly income has to be paid. Employees bi weekly payments for the health benefits is about $ 162.

The system requires at least a gross payment about $ 430 before any health benefit is deducted. Then also taxes are calculated. I expect that a gross payment of $ 162 should be enough to calculate the health benefit. Is there a legal minimum income before any benefit insurances are calculated? Any idea?

Thanks, Rita.