Collective Bargaining Agreement and Lump-Sum Contribution?

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A collective bargaining agreement calls for a regular hourly contribution to a multiemployer profit-sharing plan. A contributing Employer is having difficulty with employee retention and would like to negotiate a lump-sum payment for each employee. This mandatory payment would be made 90-180 days after the new CBA is signed and only for those actively employed on that date.  Are there any issues with this payment?

Thanks in advance.