Is it considered rude to write "black-tie" on the wedding invitations? My mom says guests won't come if they have to wear a tux.
It might be a hassle for some of your guests to rent a tux (especially if you don't run with the opera-benefit crowd), and good hostesses don't hassle their guests. A simple solution is to use the wording "black-tie invited" or "black-tie optional." That way, those who own tuxes or don't mind renting one will go ahead and wear them, and other male guests will know they should wear a nice dark suit. Mentioning the formality of your wedding will also help female guests know what they should wear. Do it that way and everyone will know that your wedding will be formal, and that they should dress appropriately -- tux or no tux.
Wedding Invitations + Wedding Stationery