I am thinking of organizing a workshop in my field and am currently in the process of looking for potential speakers. Some of these I'll be contacting for the first time ever by email. The speakers I am thinking of targeting are a mixture of experienced academics and relatively inexperienced/first-timers, such as postdocs.
Clearly we will cover travel and accommodation expenses for the speakers. Should I mention this up front in the first email, or can it be perceived as rude to do so? Is it usually taken for granted that invited speakers don't pay for travel and accommodation?