So if a private company censors speech on its platform at the bidding of a government authority, would *that* be a violation of the First Amendment?
Yes.
FACEBOOK IS A PRIVATE COMPANY IT CAN DO WHAT IT LIKES!
FACEBOOK IS A PRIVATE COMPANY IT CAN DO WHAT IT LIKES!
FACEBOOK IS A PRIVATE COMPANY IT CAN DO WHAT IT LIKES!
FACEBOOK IS A PRIVATE COMPANY IT CAN DO WHAT IT LIKES!
But to answer your question, "Yes"