From an email marketing perspective, could an invitation to a seminar be seen as a commercial solicitation? In respect to the CAN-SPAM Act, I would't think that a seminar is a product or a service, but more of a relational type of engagement.
On a side, not sure which SE site this question would best fit. The rational I am taking in count is that I am trying to think about the user's perspective (the people that may potentially receive the invitation).