Past Service Pension Adjustments (PSPA) are retroactive improvements to past service benefits. The PSPA creates a reduction in contribution room, which potentially could create a negative balance in that account. As a result, you could not claim an RRSP deduction until the contribution room became positive (through future earned income).
It is possible to withdraw funds tax-free from an RRSP to eliminate the negative balance.
Any contributions made while the the contribution room is negative would constitute an “excess contribution”.
If the negative contribution room exceeds $2,000, you must withdraw taxable RRSP funds for the difference, or else be denied entitlement to the retroactive improvements in your pension plan. The withdrawal cannot be from a spousal plan. Therefore, if all of your RRSP contributions are made spousally, you may get stuck! You also may be stuck if your RRSP investments have declined substantially, providing insufficient funds to make the withdrawal.