Freedom of choice for employers with regard to supplementary pensions

Is it desirable that employers that are bound by industry-wide pension plans are given the freedom to choose a pension provider? For defined benefit pensions with a flat rate contribution a free choice of pension provider is of no use. The flat-rate contribution leads to risk selection, hindering a proper market mechanism. For industry-wide defined contribution pension plans a free choice of pension provider may be a good option, though. It could lead to greater efficiency in the execution of pension schemes.