assumptions, changes to the legacy plan’s benefits, or changes in funding method over a period of 15 plan years beginning with the plan year in which such change in unfunded liability is incurred. The transition contribution rate for any plan year may not be less than the transition contribution rate for the plan year in which such rate is first established. (B) Multiple rates If different rates of contribution are payable to the legacy plan by different employers or for different classes of employees, the certification shall specify a transition contribution rate for each such employer. (C) Rate applicable to employer (i) In general Except as provided by clause (ii), the transition contribution rate applicable to an employer for a plan year is the rate in effect for the plan year of the legacy plan that commences on or after 180 days before the earlier of— (I) the effective date of the collective bargaining agreement pursuant to which the employer contributes to the legacy plan, or (II) 5 years after the last plan year for which the transition contribution rate applicable to the employer was established or updated. (ii) Exception The transition contribution rate applicable to an employer for the first plan year beginning on or after the commencement of the employer’s obligation to contribute to the composite plan is the rate in effect for the plan year of the legacy plan that commences on or after 180 days before such first plan year. (D) Effect of legacy plan financial circumstances If the plan actuary of the legacy plan has certified under section 432 that the plan is in endangered or critical status for a plan year, the transition contribution rate for the following plan year is the rate determined with respect to the employer under the legacy plan’s funding improvement or rehabilitation plan under section 432, if greater than the rate otherwise determined, but in no event greater than 75 percent of the sum of the contribution rates applicable to the legacy plan and the composite plan for the plan year. (E)