Yes. You should take such arrangements even if they are not obligatory.
IAS 19.61 "An entity shall account not only for its legal obligation under the formal terms of a defined benefit plan, but also for any constructive obligation that arises from the entity’s informal practices. Informal practices give rise to a constructive obligation where the entity has no realistic alternative but to pay employee benefits. An example of a constructive obligation is where a change in the entity’s informal practices would cause unacceptable damage to its relationship with employees"
