; and (B) to exempt small businesses with fewer than 50 employees from the requirements of section 102(a)(1)(F) when the imposition of such requirements would jeopardize the viability of the business as a going concern. (b) Relationship to paid leave (1) Unpaid leave for initial 10 days (A) In general The first 10 days for which an employee takes leave under section 102(a)(1)(F) may consist of unpaid leave. (B) Employee election An employee may elect to substitute any accrued vacation leave, personal leave, or medical or sick leave for unpaid leave under section 102(a)(1)(F) in accordance with section 102(d)(2)(B). (2) Paid leave for subsequent days (A) In general An employer shall provide paid leave for each day of leave under section 102(a)(1)(F) that an employee takes after taking leave under such section for 10 days. (B) Calculation (i) In general Subject to clause (ii), paid leave under subparagraph (A) for an employee shall be calculated based on— (I) an amount that is not less than two-thirds of an employee’s regular rate of pay (as determined under section 7(e) of the Fair Labor Standards Act of 1938 ( 29 U.S.C. 207(e) )