The polish social insurance financial system remains inefficient. The financial efficiency, understood as a measure of the ability to finance social security benefits from social security contributions, is decreasing. This is primarily due to the aging of the population. Therefore, a key legislative action remains the definition of the response in law to possible difficulties in the realization of social insurance benefits. The purpose of the study is to define the assumptions of a law on the formation of the financial constitution of the social insurance system. With such a law, it is also possible to introduce external monitoring of the ability to pay social security contributions and the sustainability of social insurance to cover all expenses of Social Insurance Fund. The legislature and the Constitutional Court, knowing when and in what proportion – certain expenses of the Social Insurance Fund, will not be able to be financed due to the likely reduction of the budget subsidy – can make changes in the law in advance or rule the cases of Constitutional Court that will ensure that social insurance benefits are realized to the greatest extent possible, or counteract changes in the law that increase such risks.