You may use, and personalize, the following template to help write a letter of complaint if you have experienced discrimination at a place of business. Simply copy and paste the text in your letter. Download a Microsoft Word template. 
To Whom It May Concern:
My purpose in writing this letter is to bring to your attention an experience I recently had at your place of business. It is my hope that this matter can be addressed and that you will take action to prevent other people from having similar experiences in the future.
[Explain situation and circumstances and be sure to include dates and names of persons involved.]
Often times this kind of experience is due to a lack of education about lesbian, gay, bisexual, and transgender (LGBT) diversity. As a member of the LGBT community and a frequent patron of your business, I felt I was treated unfairly and not valued as a person. I’m sure any of your LGBT employees or customers would feel the same.
One important step in countering this kind of interaction is education. I want to make you aware of an excellent LGBT-specific educational training program called Building Bridges: LGBT Diversity in the Workplace. Out & Equal Workplace Advocates, a national nonprofit organization that devotes itself to workplace equality, and is endorsed by many of the nation’s top businesses, have developed this program. The training breaks down the barriers between LGBT people and others by opening communication to foster a healthier company and workplace. You can learn more about Building Bridges: LGBT Diversity in the Workplace on the Out & Equal website at www.outandequal.org.
I ask that you seriously consider implementing a training program about LGBT people to educate your staff and create a more welcoming atmosphere. Thank you for your time and commitment to building an inclusive business. I look forward to your response.