T4 Box 50 - Pension Plan or DPSP Registration Number
Enter the seven-digit registration number we issue for a registered pension plan (RPP) or a deferred profit-sharing plan (DPSP), or the seven-digit plan identification number we issue for an unregistered foreign pension plan under which you report a pension adjustment (PA). Do this even if your plan requires only employer contributions.
However, if you make contributions to union pension funds, you have to indicate the union’s plan number, which the union has to give you. If you made contributions to more than one plan on behalf of the employee, insert only the number of the plan under which the employee has the largest PA.