Yhyjyk

This Skeptics SE post regarding a transgender individual (male to female) using a female locker room brought up some interesting legal issues regarding the rights of transgender individuals in using the locker rooms appropriate to their mental but not biological gender.

What laws apply in such cases? Are there any legal protections against abuse by non-transgender individuals, such as in this hypothetical claim by Mike Huckabee?

There are some national protections that are applicable:

Employers are legally required to provide workers reasonable access to restroom facilities. The U.S. Department of Labor's Occupational Safety and Health Administration requires that employers make toilet facilities available so that employees can use them when they need to do so, and the employer may not impose unreasonable restrictions on employee use of the facilities.

No federal, state or municipal laws or regulations specifically pertaining to gender identity require employers to utilize one type of bathroom over another, or to construct new facilities to accommodate transgender individuals.

However, some jurisdictions regulate aspects of these restrooms. For example, the District of Columbia requires single-occupant restroom facilities in any public space (e.g., restaurants) to be gender neutral -- restrooms designed for use by one individual at a time may not have a specific gender designation with "male" or "female" signage or icons -- but does not require employers to have single-occupant restrooms instead of another type.

Colorado, Washington, and Iowa allow transgender individuals the ability to use whatever gender room they wish, based on their gender identity. California is the first state to do the same for schoolchildren, according to CBS news. This is confirmed by the ACLU (#8, related information on #23), which also mentions some specific cases. Overall, there are non-discrimination laws in many - if not most - states protecting transgender men and women.

In response to Mike Huckabee's theoretical claim, from a legal standpoint, it is important to realize that laws protecting transgender people using gendered facilities consistent with their gender identity do not overwrite other laws: regardless of gender identity, sexual harassment remains sexual harassment, rape remains rape, and so on.

The provisions surrounding gendered facilities in anti-discrimination laws aim to prevent well-behaved transgender people being arrested or ticketed for simply using these facilities, e.g., Tyjanae Moore, Paula Witherspoon, Brenda Wernikoff, businesses preventing these transgender people these facilities (thereby humiliating them), e.g., Ally Robledo, Alex Wilson, River Song, and transgender people losing their jobs over bathrooms, e.g., Etsitty.

Prof. Tobais Wolff in Civil Rights Reform and the Body describes the implausibility of exploiting anti-discrimination laws for gender identity:

The purported threat that gender-identity protections pose to women in
public restrooms is twofold. The first is rape or sexual assault.
Here, the claim is that predatory men will use these laws to gain
access to their targets by “putting on a dress” and invading the
women’s bathroom.

The second purported threat is rampant
voyeurism -- a threat to women’s privacy or modesty through involuntary
exposure of the body. Here, the claim is that salacious men will use
gender-identity protections to invade women’s bathrooms and lurk
there peeping at women...

Both claims
are incoherent. For the rapist seeking available targets, of what help
could a gender-identity law be? A predator who targets women using
public restrooms would not hesitate to enter because a rule tells him
he is not allowed.

In order for these sexual predation claims to make sense, one
would have to posit that predators would lurk in public restrooms for
extended periods of time, hoping for a chance to assault a target.
Lurking is not a protected activity, whatever the gender identity of
the lurker—the enactment of gender-identity protections would not
authorize such behavior.

Aspiring voyeurs likewise have no right to lurk in
bathrooms or otherwise use them for inappropriate purposes, and a post
hoc assertion of gender identity would not provide a voyeur with any
protection—a proposition made explicit in the Connecticut legislation,
which requires a showing that “gender-related identity is sincerely
held, part of a person’s core identity or not being asserted for an
improper purpose.”

It is also argued that exploits are not happening where these laws have already been introduced.