Govt. ER to contribute to both state and private plan

[Guest cc1898]

I'm simply looking for any regs. , rules, opinions, that authorize a public employer to contribute both to its state pension system and a union fringe benefit fund. I've already found authority under the state's laws, but simply need to cite to something specific related to the Code or ERISA. Everything I've come across discusses governmental surplus or supplemental plans, and governmental plans in general. Since the fringe benefit fund would cover nonpublic employees- it's not a governmental plan. Any help is appreciated. Thanks