First of all who's the investor? Russian? And where is the hotel? In Russia?
If so, as a lawyer, I can say there is no specific names for different letters in Russia as in US. In documentry you do not need to place the precise name on it, you can just skip it.

Same can fit to US lawyers as the court would look into the content more, not the name. You can call it 'letter of request' - you not just showing interest, but requesting specific items.