Article 6 Clause 2 of the Constitution states what is considered the supreme law of the land. There is no mention Supreme Court precedents. This clause clearly states that the Constitution is the supreme law of the land and no laws whether federal or state can violate the constitution and be legally binding.
A notice of hearing is a legal document used in U.S. courts to inform individuals that the government is pursuing a an action against them. It is different than a notice of trial, which is used when individual parties are suing each other. These documents are reserved for actions in which the government is seeking redress from individuals.
It's a good idea to present a letter to the court from the witness explaining why the witness can't appear in person at the hearing. Even if the court generally permits telephone testimony from witnesses, you should ask for permission from the court in advance of the hearing.