corp to corp outsourcing

My small corp has a services contract with a large company as a subcontractor providing services to an end customer.

This large company has asked (forced) my company to enter into an agreement with a third party to ease there accounts payable load.

Can this large company force my company into a contract with a third party? Isn't this large company in fact ending our original contract by doing so. Thus, nullifying any non-compete clauses in the contract.

The large company appears to "want its' cake and eat it too" by maintaining their margins for our services and eliminating any overhead.

Any advice?

They need your permission and agreement, you are correct. Unless your current contract says otherwise.