29 USC 2652 - Effect on existing employment benefits

(a) More protective 
Nothing in this Act or any amendment made by this Act shall be construed to diminish the obligation of an employer to comply with any collective bargaining agreement or any employment benefit program or plan that provides greater family or medical leave rights to employees than the rights established under this Act or any amendment made by this Act.
(b) Less protective 
The rights established for employees under this Act or any amendment made by this Act shall not be diminished by any collective bargaining agreement or any employment benefit program or plan.