A "salaried . . . employee who is among the highest paid 10 percent of all the employees employed by [an] employer within 75 miles of the employee's worksite." 29 C.F.R. § 825.217. Under regulations promulgated pursuant to the Family and Medical Leave Act, an employer may deny job restoration to a key employee if restoration would result in "substantial and grievous economic injury to the operations of the employer." 29 C.F.R. § 825.216(b).