If the employee is enrolled in an Health Savings Account they have the option to stop and/or start contributing at any time during the plan year as they can only use what they have personally contributed to the HSA. Any unused HSA funds will roll over year to year, if the employee stops contributing at any point the funds are still available until account reaches $0.
Unlike an HSA, funds in a Flexible Spending Account are pre-funded at the time of enrollment and then deducted from the employee’s pay throughout the plan year. For this reason, an employee cannot make any changes to their FSA enrollment without experiencing a qualifying life event. Any unused FSA funds are lost if not spent by the end of the plan year.