158 ) is amended by adding at the end the following: (h) It shall be an unfair labor practice for any labor organization and any employer to enter into any contract or agreement, express or implied, whereby the organization and employer agree to modify the terms of any previous agreement in a manner that would result in a reduction or termination of retiree health insurance benefits provided to an employee or a dependent of an employee under the previous agreement, if such modification of the terms of the previous agreement occurs after the date on which the employee retires. .