29 U.S. Code § 2614 - Employment and benefits protection
The taking of leave under section 2612 of this title shall not result in the loss of any employment benefit accrued prior to the date on which the leave commenced.
As a condition of restoration under paragraph (1) for an employee who has taken leave under section 2612(a)(1)(D) of this title, the employer may have a uniformly applied practice or policy that requires each such employee to receive certification from the health care provider of the employee that the employee is able to resume work, except that nothing in this paragraph shall supersede a valid State or local law or a collective bargaining agreement that governs the return to work of such employees.
Nothing in this subsection shall be construed to prohibit an employer from requiring an employee on leave under section 2612 of this title to report periodically to the employer on the status and intention of the employee to return to work.
Except as provided in paragraph (2), during any period that an eligible employee takes leave under section 2612 of this title, the employer shall maintain coverage under any “group health plan” (as defined in section 5000(b)(1) of title 26) for the duration of such leave at the level and under the conditions coverage would have been provided if the employee had continued in employment continuously for the duration of such leave.
The employee shall provide, in a timely manner, a copy of such certification to the employer.
The certification described in subparagraph (A)(ii) shall be sufficient if the certification states that a serious health condition prevented the employee from being able to perform the functions of the position of the employee on the date that the leave of the employee expired.
The certification described in subparagraph (A)(i) shall be sufficient if the certification states that the employee is needed to care for the son, daughter, spouse, or parent who has a serious health condition on the date that the leave of the employee expired.