Employer demands I share hotel room with colleague - where do I stand?

I have to travel to a conference on behalf of my employer for 5 days/5 nights. My employer is demanding that I share a hotel room with a colleague for that time. I do not want to share a hotel room. I think I am entitled to a little personal space and privacy during a time in which I will otherwise be devoted to working on the employer's behalf. I am relatively new to the company and not particularly close to any colleagues, and value my private space. In fact the more I think about it, the more uncomfortable I get. Does anyone know if the employer is out of line for making this demand? Does Belgian labour law say anything about this sort of thing?
Thanks.