There is no federal law preventing this kind of discrimination in the work place, though there have been attempts to pass the Employment Non-Discrimination Act (ENDA). Until recently ENDA did not include provisions for gender identity. However, it has not passed Congress, and the LGBT community is sadly unprotected in the workplace.
Twenty-one states and DC prevent discrimination in the job place based on sexual orientation, but only twelve of those states and DC also include provisions for gender identity (https://hrc.org/documents/Employment_Laws_and_Policies.pdf). Although this is the right track, it is hard to comprehend how unprotected the LGBT community is in the work place. There is nothing in most states to prevent an employer from firing an employee based on their sexual orientation or gender representation. It is scary to think about, coming out of college as I am, that if I want to be protected, I must move to do so, for the basic right of maintaining my job.
Some employers, though, have taken this harsh reality into their own hands, ensuring that internally, discrimination will not be tolerated. The Human Rights Campaign creates a list each year of the most welcoming employers with the best policies (http://www.hrc.org/issues/best-places-to-work-2011.htm). When searching for a job in unprotected states, it is important to try to find a safe and welcoming place. If you don’t want to move to ensure the safety of your eye, it is important to research the companies to which you are applying. Often on the page where their openings are listed, there will be a disclaimer about their discrimination policy.
It would be ideal if we did not have to take these precautions, if people were not so ignorant, but until laws are passed, there is no way to ensure the stability of a job for a dependable worker if that worker has a differing sexual orientation or gender identity. Keep in mind that there are options, but it is important to be aware of the issues facing us. Perhaps with the repeal of Don’t Ask, Don’t Tell, a progression is coming to the remainder of the world of employment.