This is a good boilerplate letter from Linda Bacon, author of Health at Every Size, that you can adapt if your workplace (or local government, or other organization you are involved in) has an "anti-obesity" campaign.
http://healthateverysizeblog.wordpress.com/2012/03/20/the-haes-files-de-stigmatizing-our-workplaces-a-start/
http://healthateverysizeblog.wordpress.com/2012/03/20/the-haes-files-de-stigmatizing-our-workplaces-a-start/