Is a supplementary retirement plan in employment considered usury?

The governmental retirement system is permissible if the subscribers' funds are not placed in interest-based banks or invested in prohibited activities, and if the solidarity is optional, it must be abandoned if there are impermissible elements. However, if it is mandatory, the subscriber must dispose of the percentage of money equivalent to the usurious interest upon receipt. The retirement system for private companies is not permissible due to its inclusion of gharar (excessive uncertainty). Supplementary retirement is permissible if the original system is permissible, as it is a payment of installments before their due date.