No amendment of a plan which increases the liabilities of the plan by reason of any increase in benefits, any change in the accrual of benefits, or any change in the rate at which benefits become nonforfeitable under the plan shall be adopted if a waiver under this subsection or an extension of time under section
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(d) is in effect with respect to the plan, or if a plan amendment described in subsection (d)(2) which reduces the accrued benefit of any participant has been made at any time in the preceding 12 months (24 months in the case of a multiemployer plan). If a plan is amended in violation of the preceding sentence, any such waiver, or extension of time, shall not apply to any plan year ending on or after the date on which such amendment is adopted.