Which are auxiliary verbs in the sentence a new law must be passed before tomorrow?

The auxiliary verbs in the sentence "A new law must be passed before tomorrow" are:

* must - This is a modal auxiliary verb, indicating obligation or necessity.

* be - This is a form of the verb "to be" and acts as a helping verb in the passive voice construction "be passed".

So, the sentence uses two auxiliary verbs to create the passive voice and express a sense of obligation.