Delivered by hand directly to the addressee, the body of the letter is plainly written in a different hand from the signature, suggesting the Chief Warlock either dictated the missive or abdicated entirely the burden of writing it.

25th February, 1892
Lord Phillip Darlington,
9th Viscount Winfield
It has come to the attention of the honourable members of the Wizengamot that you have recently announced an engagement—felicitations on your news. Your choice of bride, however, does give this body pause, and so it is insisted that you put a halt to any nuptial planning until further notice.
As you may be aware, Miss Acacia Q. Ruskin is the product of interbreeding between a human father and a vampiric mother. While it is not the intention of this body to prevent those who might be considered witches and wizards, by virtue of their magical bloodlines, to wed similarly-identified people, your own case is a special one.
As you are certainly aware, the relationship of the Ministry of Magic—and, indeed, the magical world as a whole—with Her Majesty, Queen Victoria and the muggle realm in which she governs is a tenuous one at best. Your position as Viscount Winfield necessitates your straddling of the two worlds. We the Wizengamot are concerned that introducing vampiric blood into such a well-regarded (and deeply public) muggle bloodline represents, at best, a threat to the International Statute of Secrecy and, at worst, a danger that would cause the events of 1877 to appear a minor inconvenience in comparison.
Due to the uniqueness of the situation, we are assembling a panel to hear your case. The date of this hearing has been scheduled for Tuesday, 29th March and will involve stakeholders from various Ministry departments. You will, of course, be expected to attend, and Miss Ruskin may submit a written statement to be read aloud during the proceedings.
Please be advised that no marriage license will be granted by the Ministry of Magic in regards to this union until the matter is resolved. Should either party seek to skirt around this edict, the Wizengamot will have no alternative but to issue a warrant for your arrest and that of Miss Ruskin, as well as inform Her Majesty in full.
Your cooperation and patience in this matter is appreciated.
Chief Warlock of the Wizengamot
— Phillip Darlington —

— phenomenal set by bex! —