69.1. Until it is determined under an actuarial valuation the date of which is after 14 December 2009, the portion of the employer contribution of which an employer may be relieved under section 42.1 of the Act may not exceed an amount corresponding to the amount obtained by multiplying by 20% the difference, established at the date of the last actuarial valuation of the pension plan, between the assets and liabilities of the plan, determined on a solvency basis.