While legal considerations might be your biggest worry, making your site more accessible is simply good customer service. More than 39 million Americans are blind and another 246 million have "low vision," Another one million are deaf in the U.S. Add to that people with mobility issues that prevent them from using their hands and that's a huge portion of the country's buying power.
If you return your availability by room type your our online booking engine must also display and hold accessible rooms only for people with disabilities until all other rooms have been booked. (Rule becomes effective March 15, 2012.) If you return your availability by individual units you do NOT have to hold ADA rooms back until all other units have been reserved. However, all other ADA regulations do apply (ADA room descriptions, using a booking engine that is ADA compliant, and making your website ADA accessible).
The ADA is the Americans with Disabilities Act, passed almost 30 years ago in 1990. This act was originally put in motion pertaining solely to physical location. It requires establishments to provide people with disabilities easy access to various levels throughout the business. This act was set to achieve an equal experience to all people, handicapped or not.