Correct. Only 17 states protect against gender identity discrimination in the private sector. The Wikipedia article has a nice map of what is protected by state: https://en.wikipedia.org/wiki/LGBT_employment_discrimination...

Attempts to prohibit discrimination of sexual orientation and gender identity at the federal level (the same as sex, age, handicap, race, color, religion or national origin) via the Employee Non-Discrimination Act (ENDA) have failed since 1994. See https://en.wikipedia.org/wiki/Employment_Non-Discrimination_... for details.