((a)) ** Allowance of deduction** There shall be allowed as a deduction for the taxable year an amount equal to the amount—

((1)) which is contributed by an employer to a trust described in section 501(c)(22) (relating to withdrawal liability payment fund) which meets the requirements of section 4223(h) of the Employee Retirement Income Security Act of 1974, and

((2)) which is properly allocable to such taxable year.

((b)) ** Allocation to taxable year** In the case of a contribution described in subsection (a) which relates to any specified period of time which includes more than one taxable year, the amount properly allocable to any taxable year in such period shall be determined by prorating such amounts to such taxable years under regulations prescribed by the Secretary.

((c)) ** Disallowance of deduction** No deduction shall be allowed under subsection (a) with respect to any contribution described in subsection (a) which does not relate to any specified period of time.