"Because practically all Taft-Hartley plans originated among unions and employers in the private sector, they are subject to ERISA and participants' benefits are, to some extent, 'insured' by the [PBGC].... What surprises many cities and special districts that participate in these trusts is that, under certain circumstances, the trusts can and must require the participating employers to contribute additional sums -- above and beyond what is called for in the applicable [Memorandum of Understanding]."  MORE >>