I would disagree with ERISAAPPLE. The plan document governs the plan. The CBA governs the relationship between employer and employee. The CBA may call for benefits to be provided, but it is a contractual obligation of the employer's to figure out how to accomplish it. If the plan does not reference the benefits promised in the CBA in such a way that it becomes part of the plan documents, the employer is in breach of the CBA, but the plan document should still govern the plan.
It is fixable, however....