Who owes vacation pay upon separation, union or employer?

I only want to hear from people who KNOW California state labor laws please. It is my understanding it is the employer who owes vacation pay for normal "at will" employees. However, this involves a union. I've recently discussed this case with Deputy Labor Commissioner of California and a law firm who both told me that it is the union who owes unpaid vacation pay. The collective bargaining agreement stipulates who is owed, but not by whom. The union says to talk to the state about going after the former employer. But, again, the state says it's the union who owes. The NLRB is not helpful because it's past their statute of limitations. What should happen in this case? Thank you for your input.